An Arma 3 “server version mismatch” means your client and the server are not presenting the same compatible game data. Match the game branch and build first, then repair base-game files, synchronize every required Workshop mod, and only afterward investigate the server installation or network path. This order identifies whether the problem belongs to you, Steam, a mod maintainer, the server administrator, or a firewall.
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What an Arma 3 server version mismatch actually means
Arma 3 does not compare only the number shown beside the game in Steam. A join attempt can fail when the client and server differ in the executable build, the selected release branch, a required add-on, a mod revision, or the data loaded from disk. A connection can also be blocked after all software matches if a firewall or another network obstacle prevents the session from completing.
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Bohemia Interactive identifies three broad connection categories: a different game version (including an experimental-development server versus the normal build), required user-made add-ons or mods, and firewall or other connection problems. In practice, the useful diagnosis is more specific:
| Comparison axis | What has to be compatible | Usual owner | First check |
|---|---|---|---|
| Game branch and build | Client and server must run the same compatible Arma 3 branch and current build. | Player and server administrator | Check whether either side uses the normal release or experimental-development branch, then update both installations. |
| Base-game file integrity | Core files must not be damaged, partially updated, or different from Steam’s current version. | Player or server administrator | Run Steam’s “Verify integrity of game files.” |
| Workshop mod identity and revision | Every required mod must be present, enabled, and at the revision expected by the server. | Player, mod maintainer, and server administrator | Read the server’s required-mod list and let the Arma 3 Launcher download missing Workshop items. |
| Server installation and mod path | The dedicated server must load its own intended files, not data from another Arma installation. | Server administrator | Inspect the launch configuration, including the -mod= parameter. |
| Network reachability | Traffic between your computer and the server must pass through local and upstream firewalls. | Player, server, or network administrator | Check firewall rules only after branch, files, and mods are aligned. |
The distinction matters because changing a firewall cannot repair an old PBO, and downloading a mod cannot correct a dedicated server that was never updated after a game patch.
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Fix the mismatch as a player
Follow these steps in order. After each major change, try the same server again. Changing several variables at once makes it difficult to tell which one solved the problem.
1. Close Arma 3 and restart Steam and the launcher
Exit the game completely. Quit Steam rather than leaving it running in the notification area, start it again, and then restart the Arma 3 Launcher. Pending game patches or Workshop downloads can remain incomplete while the game or launcher is open. Wait for Steam’s downloads to finish before checking the server list.
If Steam reports that an update is queued, paused, or waiting for disk allocation, allow that operation to complete. Launching Arma 3 before the update finishes can leave the executable and its data at different revisions, which is enough to trigger a mismatch even when the title appears installed.
2. Match the server’s release branch
Ask the administrator which branch the server uses, or read the branch information shown in the server’s community description. The normal release and the experimental-development branch are not interchangeable. Bohemia specifically warns that an experimental-development server can differ from the normal game build.
In Steam, open Arma 3’s properties and inspect the branch or beta selection. Select the same branch that the server requires, allow Steam to download the corresponding files, and restart the launcher. If the server has moved back to the normal release, return your client to that branch instead of keeping an experimental option selected from an earlier test.
Do not infer branch compatibility from the server’s name alone. A server can retain an old description while its administrator changes branches, and a community may operate separate servers on different branches. When the administrator cannot confirm the branch, test a known server that uses the normal release; this separates a local branch selection from a server-specific configuration.
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3. Verify the base-game files in Steam
Use Steam’s file check before reinstalling the entire game:
- Open Steam and go to your Library.
- Right-click Arma 3 and choose Properties.
- Open Installed Files.
- Select Verify integrity of game files and wait for the process to finish.
- Restart Steam or the Arma 3 Launcher if Steam replaces files, then try the server again.
Bohemia recommends this check for damaged or inconsistent data. Verification can restore core files, but it does not guarantee that a Workshop mod is at the server’s required revision; mod-specific errors need the Workshop steps below.
If verification reports files that must be reacquired every time you launch, note the filenames and the Steam library location. A full disk, permissions problem, security software quarantine, or an unstable drive can prevent Steam from keeping repaired files. Those conditions require local Windows or hardware troubleshooting rather than repeated server reconnects.
4. Synchronize every required Workshop mod
Open the server entry in the Arma 3 Launcher or server browser and inspect its required add-ons. Enable every required Workshop mod, not only the ones you remember using on a previous visit. Let the launcher subscribe to and download missing items before pressing Play.
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Check the mod’s displayed revision after downloading. Two items with similar names can be different projects, and a server may require a particular collection or dependency. Use the identifier supplied by the server rather than guessing from a search result. If the administrator has changed the collection, remove obsolete entries from the launch preset and recreate the preset from the current server list.
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When a server starts without mods but fails with mods enabled, that result points to mod identity, revision, load order, or a dependency rather than the base-game branch. Report the exact mod name and revision to the administrator; do not upload a replacement file from an unofficial source, because the server may use a signed release that your substitute cannot match.
5. Repair a named PBO or BISIGN error
A PBO error is more specific than a generic mismatch. Bohemia’s known-issues guidance says that an inability to join because of a PBO error means the server is using different data from your client. A PBO is an Arma data archive; a BISIGN file is the accompanying signature used with signed content.
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When the error names a file, record its exact path and filename. Then:
- Exit Arma 3 and the launcher.
- Delete the named local PBO and its accompanying BISIGN file. Delete only the files identified by the error, not an entire installation or Workshop folder.
- For a base-game file, run Verify integrity of game files in Steam.
- For a Workshop mod, re-download the item from Steam Workshop and allow the launcher to rebuild its local copy.
- Start Arma 3 again and retry the same server.
This is the prescribed recovery for a damaged or inconsistent local copy. If the same PBO error returns after a clean verification or Workshop download, the server may be running a different copy. Contact the server administrator with the full PBO name; the administrator may need to update or clean the server-side data.
Do not “fix” a signature error by renaming a file, removing every BISIGN file, or disabling signature checks. Those actions can hide the specific mismatch and may prevent the server from accepting any properly signed content.
6. Check firewalls only after software matches
If branch, build, base files, and required mods are aligned but the join still fails, investigate connectivity. Bohemia lists firewalls and other obstacles between the player and server as a separate cause.
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- Confirm that your operating system firewall allows Steam and Arma 3 to communicate on private or trusted networks as appropriate for your setup.
- Check whether security software recently quarantined or blocked an Arma 3 executable after an update; restore the application rule rather than allowing an old executable only.
- If you are on a school, workplace, hotel, or shared network, ask its administrator whether multiplayer traffic is filtered.
- Give the server administrator the time of the failed attempt and the exact error. The administrator can compare your failure with other players and inspect the server’s own firewall or hosting network.
A browser listing that appears normally does not prove that the full game session can pass through every firewall. Conversely, a timeout without a version or PBO message does not prove that your files are wrong; it is the point at which network testing becomes useful.
How to tell which side must make the change
Signs the problem is on your client
- Steam shows a queued update, or the launcher reports a missing Workshop download.
- You selected the experimental-development branch while the target server uses the normal release, or the reverse.
- Verification replaces files, or a named PBO/BISIGN error disappears after a local re-download.
- Other players can join the server while your machine alone reports the mismatch.
Complete the player sequence, then tell the administrator exactly which step changed the result. This gives the administrator a reproducible state instead of a general “it will not connect” report.
Signs the server needs attention
- Several players receive the same mismatch immediately after an Arma 3 patch.
- Your client is on the confirmed branch, passes verification, and has the exact required Workshop revisions, yet the same PBO error remains.
- The server’s advertised mod list differs from the list it actually sends to the launcher.
- The administrator recently moved or copied the dedicated-server files.
Bohemia has documented a false version-mismatch report that was resolved by updating the dedicated-server installation. An administrator should therefore update the server after game patches before asking every player to reinstall or delete local files.
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Signs the problem is network-related
- The server appears in the browser, but the connection times out or is rejected without identifying a version, mod, PBO, or signature.
- You can join other servers with the same branch and mod set, while the target server is unreachable for multiple players on your network.
- Changing networks changes the result without changing your Arma installation.
At this stage, preserve the successful software configuration and have the server or network administrator inspect firewall and routing rules. Re-verifying files repeatedly will not open a blocked connection.
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Update the dedicated installation after every game patch
Run the update process for the dedicated-server installation whenever the Arma 3 client receives a patch. A server that continues running an older executable or data set can present a version-mismatch message to otherwise current players. Restart the server after the update and verify that the process is using the updated directory, not a second copy left on the machine.
When troubleshooting a report that began immediately after an official patch, compare the server’s update time with the patch deployment. The documented false-mismatch case required updating the server; asking players to delete valid local files would not correct an outdated server.
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Prevent data from the wrong Arma installation loading
A host can have a full client installation, a dedicated-server installation, and one or more test copies. If the launch configuration searches the wrong location, the server may load client add-ons or stale data even though the dedicated-server files themselves are current.
The dedicated-server documentation recommends an explicit empty -mod= workaround when the server accidentally loads full-client data from another installation. Apply that workaround when the server should start without implicit local mods, then restart and inspect the startup output. An explicit empty value is different from omitting the parameter: it tells the launch configuration not to inherit a mod path from another installation.
Use an explicit mod list when the server requires add-ons
For a modded server, use an explicit -mod= list that points to the intended server-side add-on directories. Bohemia’s known-issues guidance also recommends an explicit -mod= list when add-ons load from the wrong installation. Keep the list synchronized with the Workshop identifiers presented to players, and remove obsolete paths after a migration.
Do not solve a path problem by copying an entire client directory over the server. That can introduce unrelated data and make future updates ambiguous. Keep the dedicated installation separate, document its mod directories, and ensure the service or shortcut starts the same executable and configuration every time.
Validate the server’s advertised requirements
After changing the launch configuration, test from a clean client profile or ask a player who has not recently joined the server to connect. Confirm that the launcher receives the intended required-mod identifiers, that each item downloads, and that no PBO error names a server-only or obsolete file. If the server uses a private or locally built add-on, provide players with the exact distribution method and revision; a public Workshop search result is not a substitute for a matching private build.
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A practical decision path for recurring errors
- Record the exact message. “Version mismatch,” a named PBO, a BISIGN/signature message, a missing mod, and a timeout point to different checks.
- Confirm branch and update state. Compare normal release versus experimental-development and finish all Steam downloads on both client and server.
- Repair the base client. Verify Arma 3 files in Steam and relaunch.
- Rebuild the mod set. Enable every required Workshop item, download missing content, and remove stale entries from the launcher preset.
- Apply the named-file repair. Delete only the PBO and accompanying BISIGN identified by the error, then verify or re-download.
- Escalate with evidence. Send the administrator the branch, exact error, PBO filename if present, and the fact that verification and Workshop synchronization completed.
- Inspect network rules last. If the software state is confirmed identical, check local, host, and upstream firewalls.
This sequence avoids the most common wasted effort: changing firewall rules for a branch mismatch, reinstalling the game for a server-side PBO discrepancy, or repeatedly downloading a mod when the dedicated server is still running an old build.
Preventing the mismatch from returning
For players
- Leave Steam updates enabled and allow Workshop downloads to finish before launching.
- Keep separate launcher presets for servers that use different mod collections or branches.
- Before joining a newly updated community server, open its required-mod list and let the launcher reconcile it rather than relying on an old preset.
- Keep the exact PBO/BISIGN filename when reporting an error; administrators can act faster with that detail.
For administrators
- Update the dedicated-server installation promptly after every Arma 3 patch.
- Keep the dedicated installation separate from any full client installation.
- Use an explicit empty
-mod=when the server should load no implicit client mods, or an explicit list when it should load defined add-ons. - Publish current Workshop identifiers and remove retired revisions from the server configuration.
- After maintenance, test a join with the same branch and mod set used by regular players.
The reliable fix is not a single reinstall command. It is alignment across five independent layers: branch and build, base files, Workshop content, server paths, and network reachability. Check them in that order and assign each remaining problem to the person who controls that layer.
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