MDT error 0x800405 does not have one confirmed, universal Microsoft meaning. The same hexadecimal value is used by unrelated software, so the reliable fix is to identify the executable or task-sequence step that produced it. Capture the full message and logs, then inspect the deployment answer file if the failure occurs while creating partitions. Correct UEFI/BIOS partition definitions and Windows/recovery role assignments before rebuilding the deployment. If the error belongs to a different application, follow that application’s remedy instead of changing MDT files blindly.
Why 0x800405 is difficult to diagnose
A hexadecimal code is useful only in the context that emitted it. A broad search found no Microsoft Learn article or official MDT reference that defines 0x800405 as a canonical MDT error. Treat the “MDT” label as unverified until you know which executable, task-sequence action, or setup component displayed it.
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The number is not globally unique. Dialogic’s error table assigns 0x800405 to an “Internal MMDL Macro Error” in its PLAY subsystem and recommends redownloading the board and restarting the application. That is a Dialogic-specific remedy, not an MDT partitioning fix. If the message came from Dialogic software, stop troubleshooting MDT and use that product’s recovery procedure.
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Capture the failure before changing anything
Do not immediately rebuild the deployment share, delete the answer file, or run a generic “repair” utility. First preserve the evidence that identifies the component. Write down the following while the error is visible:
- The complete error line, including any text before or after
0x800405. - The executable name or task-sequence step shown in the dialog or log.
- Whether the failure occurred in Windows Preinstallation Environment (WinPE) or after Windows had booted into the full operating system.
- The deployment platform: Microsoft Deployment Toolkit (MDT), Configuration Manager, VMware unattended setup, or another product.
- The Windows edition and image/build being deployed.
- The exact action in progress, such as disk preparation, partition creation, image application, driver injection, software installation, or first boot.
- The time of the failure, including the time zone, so you can correlate entries across logs.
Keep the original answer file, task-sequence export, image, and log files. Make a working copy before editing anything. A before-and-after comparison is often more useful than a large batch of unrecorded changes.
Use the context to choose the correct troubleshooting branch
| Observed context | What it suggests | First action |
|---|---|---|
| Partition creation fails during unattended setup or in VMware | Answer-file disk layout, firmware mode, or partition-role assignments may be wrong | Inspect the answer file and verify UEFI/BIOS system partitions and role order |
| A named MDT task-sequence step fails in WinPE | The failing action, its variables, or an earlier step may be responsible | Correlate the timestamp with LiteTouch, Bootstrap, WinPE, and setup logs |
| The error appears after Windows starts | A full-OS setting, installation, uninstallation, shutdown, or damaged system element may be involved | Review recent system changes and logs from the same time |
| A Dialogic PLAY application displays the code | The code belongs to Dialogic’s MMDL subsystem, not MDT | Redownload the board and restart the application |
| No executable, step, or deployment phase can be identified | The code alone is insufficient to select a safe fix | Reproduce once with logging enabled and capture the complete message |
Fix partitioning and unattended-setup failures
The clearest deployment-specific report associated with this number involved an unattended Windows installation in VMware that failed while creating a partition. The response identified an incorrectly built answer file: it did not define the required UEFI or BIOS system partitions, and it assigned the Windows and recovery roles incorrectly. Rebuild the file from documented answer-file instructions rather than trying to patch a single line at random.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problems1. Confirm the virtual machine’s firmware mode
Determine whether the VMware machine is configured to boot with UEFI or legacy BIOS. The answer file must describe a disk layout appropriate to that mode. A layout designed for one firmware mode can fail when setup is started in the other, even when the Windows image itself is valid. Record the firmware setting before editing the file so you can reproduce the test.
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2. Check that the disk layout contains the required system partitions
Open the working copy of the answer file and inspect its disk-configuration section. For UEFI deployments, verify that the layout includes the system partitions expected by the documented Windows setup design. For BIOS deployments, verify the corresponding BIOS system arrangement. Do not copy a UEFI layout into a BIOS deployment or vice versa, and do not remove a system partition merely because the Windows partition is present.
The evidence does not establish universal partition sizes or a single layout for every Windows edition, so use the layout required by your deployment’s documented instructions and image requirements. The important checks are that the partitions exist, appear in a valid order, use the intended types, and are created on the disk that setup is actually targeting.
3. Verify Windows and recovery roles
Check every role assignment in the answer file. The partition intended for Windows must be assigned as the Windows destination, while the recovery partition must be assigned its recovery role. Swapping those roles can cause setup to apply files to the wrong volume or fail before the image is applied. Confirm that each role points to the intended partition number after the layout is created; do not rely on drive letters alone in WinPE.
4. Rebuild rather than layering uncertain edits
If the file has been copied between projects or edited repeatedly, create a clean version from the documented instructions for the selected firmware mode. Preserve the old file under a different name for comparison, then change only the disk-layout and role definitions that are known to be incorrect. Keeping unrelated settings unchanged makes the next test meaningful.
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5. Test the same path in VMware
Use a disposable virtual machine or a snapshot so a failed partition operation cannot destroy a production deployment. Attach the same Windows image, boot mode, and answer file used in the failing run. Confirm that the partitioning step completes before adding later task-sequence actions. If the error returns, capture the new timestamp and compare the logs with the original run instead of making several simultaneous edits.
Investigate task-sequence and full-OS causes
When the error is attached to a task-sequence label rather than a partition operation, several classes of change have been reported as possible contributors:
- Incorrectly configured system or deployment settings.
- Invalid system entries left by a previous change.
- A software installation or uninstallation that did not complete correctly.
- An improper shutdown during setup or a prior deployment step.
- Missing or damaged system files.
These categories are starting points for evidence gathering. They do not justify deleting registry entries, replacing system files, or rerunning the entire deployment without identifying the failing component.
Review the last controlled change
Compare the failing run with the last known-good run. Identify whether a package, application, driver, answer-file edit, task-sequence condition, or image revision was introduced. Temporarily return one item to the known-good version and test the same step. If the error disappears, keep the change isolated and validate it separately rather than combining it with other updates.
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Check installation and uninstallation steps
If the failure follows an application install or removal, verify that the command completed, returned the expected exit state, and did not leave the task sequence waiting for an interactive prompt. Review the step’s conditions and working directory as recorded in the deployment logs. A failed earlier action can make a later step appear to be the source of 0x800405, so follow the first error in time order.
Account for improper shutdowns
Record whether the machine, virtual machine, or deployment host was powered off or reset during the previous run. Restart cleanly, allow pending setup operations to finish, and repeat the test from the same checkpoint. Do not treat a clean restart as proof that the underlying answer file or task-sequence configuration is correct; it only removes an interrupted-run variable.
Separate system-file symptoms from deployment configuration
When the same error appears in the full operating system outside the deployment sequence, note which Windows component reports it and whether other system-file errors occur. A damaged system element may require Windows servicing or restoration from a known-good image, while a deployment-only failure points back to the task sequence or answer file. Keep those paths separate so a repair to one environment does not obscure the other.
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Use the log family that matches the phase of the failure. Deployment Workbench and task-sequence logs can show the action name and variables; LiteTouch and Bootstrap logs can show how the deployment was launched; WinPE and Windows setup logs can reveal partitioning and image-application failures. The names and locations vary with the deployment arrangement, so search the deployment share, boot media, and target machine for the corresponding logs rather than assuming a single fixed path.
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- Record the time displayed with the error.
- Open the log generated by the active phase: Deployment Workbench, LiteTouch, Bootstrap, WinPE, or Windows setup.
- Search for
0x800405, then read the preceding entries for the first failed command, partition operation, or component load. - Identify the executable, task-sequence step, disk number, and answer-file setting associated with that first failure.
- Compare the same section with a successful run, if one exists.
- Save both versions before changing the deployment so you can demonstrate which edit altered the result.
A log that contains only the hexadecimal value, without a task name or preceding failure, is not enough to select a repair. In that case, increase logging for the next controlled reproduction and capture the complete message from the first component that stops.
Retest one change at a time
After identifying a likely cause, make one reversible change and run the same deployment path. Examples include replacing the answer file with a clean firmware-matched version, correcting one Windows/recovery role assignment, restoring one package to its prior revision, or removing one newly added task-sequence condition. Keep the original files and logs, and note the exact change and result.
If the step succeeds, repeat the test from a clean snapshot to rule out a one-off state. If it fails again, revert the change and choose the next hypothesis supported by the logs. Avoid changing partition layout, task-sequence logic, image contents, and host firmware in one pass; that prevents you from knowing which change mattered.
When the code is not an MDT error
Because 0x800405 is reused, verify the product name in the dialog title, event source, or executable path. A Dialogic PLAY error is documented as an internal MMDL macro error and has a product-specific remedy: redownload the board and restart the application. Applying that instruction to an MDT deployment would not correct an answer-file problem. Conversely, rebuilding an MDT answer file cannot repair a Dialogic board or application state.
If the code appears in another vendor’s software, use that software’s error table and logs. Do not infer that every occurrence is related to Windows deployment merely because the number matches.
Quick Recap
Common mistakes that make diagnosis harder
- Searching only for the number. The code is ambiguous without the emitting component.
- Assuming a partition failure is an image failure. An incorrect answer file can stop setup before the image is touched.
- Mixing firmware modes. A UEFI layout and a BIOS layout are not interchangeable.
- Swapping partition roles. Windows and recovery assignments must point to their intended volumes.
- Editing the only copy of the answer file. Preserve the original so you can compare and roll back.
- Changing several variables at once. Multiple edits eliminate the evidence needed to identify the cause.
- Ignoring phase boundaries. WinPE, Windows setup, and the full operating system produce different logs and have different failure modes.
- Treating a third-party scan as an official MDT diagnosis. A utility can provide an additional Windows check, but it cannot establish which task-sequence component emitted the code.
A repeatable checklist
- Copy the complete message and note the executable or task-sequence step.
- Record WinPE versus full-OS phase, deployment platform, Windows image, firmware mode, and timestamp.
- Preserve the answer file, task-sequence export, image, and original logs.
- If partitioning failed, rebuild the answer file with the correct UEFI or BIOS system partitions.
- Confirm that partition order, types, and Windows/recovery role assignments are correct.
- Correlate the timestamp across Deployment Workbench, LiteTouch, Bootstrap, WinPE, and setup logs as applicable.
- Review the first preceding failure and the last known-good configuration.
- Apply one reversible change, rerun the identical path, and record the result.
- If the message belongs to unrelated software, stop changing MDT and follow that product’s documented remedy.
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