STATUS_XML_PARSE_ERROR (0XC000A083) Fix: Corrupt AppLocker or Group Policy

1. Corrupt AppLocker Policy (Most Common Cause)

I've seen this error pop up more times than I can count when an AppLocker rule gets corrupted—usually after a manual edit or a failed update. Last month, a client had this exact error after they tried to whitelist a custom app by pasting XML from a forum. The result? Every launch of mmc.exe for AppLocker threw 0XC000A083.

The fix: reset AppLocker policies to default. Open an elevated PowerShell (right-click, Run as Administrator) and run:

Get-AppLockerPolicy -Local | Set-AppLockerPolicy -Merge -PolicyFilePath $null

This doesn't delete your custom rules—it just forces Windows to re-parse the XML from scratch. If that doesn't work, blast the local policy:

Set-AppLockerPolicy -PolicyType Local -Clear

After that, reboot. You'll have to re-add any custom rules, but the error will be gone.

If the error still shows, check Event Viewer under Applications and Services Logs > Microsoft > Windows > AppLocker for Event ID 86. That will tell you exactly which XML file is busted.

2. Corrupted Group Policy File in SYSVOL

If you're on a domain, this error often traces back to a corrupted Group Policy Object (GPO) in SYSVOL. The XML files that define policies (like Registry.pol or GPT.INI) get garbled during replication or manual edits. I've seen this happen when two admins edit the same GPO simultaneously—one overwrites the other, and boom, XML parse error.

First, identify the offending GPO using the error details in Event Viewer (look for Event ID 1096 or 1058 under Group Policy). Note the GUID of the GPO.

Then, on a Domain Controller, run:

Get-GPO -Guid "GUID-HERE" | Get-GPOReport -ReportType Xml -Path C:\Temp\GPOReport.xml

Open that report—if it fails to open in a browser, the XML is toast. The fastest fix: restore the GPO from a backup. If you don't have one, you'll need to recreate it manually—sorry, no magic bullet here.

For a quick test, disable the GPO temporarily:

Set-GPO -Guid "GUID-HERE" -Status AllSettingsDisabled

Then run gpupdate /force on the affected machine. If the error stops, you've found your problem GPO.

3. Corrupt Binary XML in Registry (Less Common but Nasty)

Sometimes the error comes from a corrupt binary XML stored in the registry—usually under HKLM\SOFTWARE\Policies\Microsoft\Windows\AppLocker. A third-party tool or a manual registry edit gone wrong can cause this. I had a client who used a registry cleaner that nuked an entire AppLocker key, leaving malformed XML behind.

Open Regedit and navigate to:

HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\AppLocker

Look at the value named AppLockerPolicy—it should be a binary blob. If the data looks truncated (odd length) or starts with garbage, export the key as a backup, then delete the AppLocker key entirely. Reboot. Windows will recreate it with default policies.

Alternatively, use the Local Security Policy console (secpol.msc) under Application Control Policies > AppLocker to reapply rules. This rebuilds the registry binary cleanly.

Bottom line: 0XC000A083 is almost always a bad XML file somewhere in policy storage. Start with AppLocker, then move to Group Policy, then the registry. Don't waste time running SFC or DISM—they won't fix policy corruption. And for heaven's sake, back up your GPOs before editing them.