Fix ERROR_SXS_INVALID_ASSEMBLY_IDENTITY_ATTRIBUTE 0X000036C1

Quick answer

Reinstall or repair the application throwing this error. Run sfc /scannow and DISM /Online /Cleanup-Image /RestoreHealth from an admin command prompt to rule out system file corruption.

What's actually going on

This error shows up because Windows can't parse the assembly identity attribute in a manifest file. That manifest is usually embedded inside the EXE or sitting next to it as a .manifest file. I had a client last month whose accounting software wouldn't launch after a botched update. Event Viewer pointed straight to this error code. The manifest had a typo in the processorArchitecture field — someone wrote X86 instead of x86. Windows said nope.

The error triggers when you launch a program, and Windows' side-by-side (SxS) loader hits that malformed attribute. Common triggers: bad app install, partial update, or a corrupted Windows component store. You'll see it in Event Viewer under Windows Logs > Application with event ID 33 or 63.

Fix steps

Check Event Viewer for the exact faulting app. Open Event Viewer (eventvwr.msc), go to Windows Logs > Application, and search for event ID 33 or 63 with source SideBySide. It'll tell you which EXE and manifest file is broken.
Reinstall the application. Uninstall it from Control Panel, reboot, then download a fresh copy and install. 9 times out of 10 this fixes it because the bad manifest gets replaced.
Repair the application. If a reinstall isn't practical (custom LOB app, no installer), try a repair. Go to Settings > Apps > find the app > Modify > Repair. Some installers let you run the setup again and choose Repair.
Run system file checks. Open an admin command prompt and run:
```
sfc /scannow
```
```
DISM /Online /Cleanup-Image /RestoreHealth
```
Wait for both to finish, reboot, and test the app.
Manually fix the manifest file (advanced). If you know which manifest is wrong (Event Viewer gives the path), open it in Notepad. Look for the <assemblyIdentity> element. Common screw-ups: processorArchitecture="X86" (should be lower-case x86), type="win32" (should be win32 without quotes), or version attribute like 1.0.0.0 missing a field. Fix the typo, save, and relaunch the app. But be careful — one wrong character and you'll make it worse.

Alternative fixes if the main one fails

System Restore. Roll back to a point before the error started. Type rstrui.exe in the Start menu and pick a restore point.
Use Compatibility mode. Right-click the EXE, go to Properties > Compatibility > Run compatibility troubleshooter. Sometimes forcing an older Windows version bypasses the bad manifest.
Update or roll back .NET Framework. Some apps depend on .NET, and a corrupted .NET manifest can throw this error. Check Windows Update for .NET patches, or uninstall the latest .NET update if it started after a recent update.
Clean boot. Disable all non-Microsoft startup items and services via msconfig. If the app works, a third-party service is messing with the SxS loader.

Prevention tip

Never edit manifest files on a whim. If you're a developer building apps for clients, validate your manifests with mt.exe (part of the Windows SDK) before distributing. For everyone else: keep Windows updated, avoid beta software on production machines, and always have a backup of app installers. One corrupt manifest can tank your whole morning.