Fix 0x36FB Assembly Public Key Too Short

Windows can't load an app because an assembly's public key is too short. Try the registry tweak first, then re-register the component, or rebuild the cache if needed.

What This Error Actually Means

You're staring at ERROR_SXS_PROTECTION_PUBLIC_KEY_OO_SHORT (0X000036FB) and wondering why your app won't launch. I know this error is infuriating — it usually pops up right when you need to finish something important.

The short version: Windows uses something called side-by-side assemblies (the SxS folder) to share code between apps. Each assembly has a public key, and Windows checks that key's length before it trusts the code. When the key is too short, Windows assumes the assembly is tampered with or corrupt and blocks it. This often happens after a botched update, a third-party cleanup tool, or when you manually copied files from an older system.

Here's the kicker: the fix depends on whether the assembly is system-related or app-specific. I'll walk you through three fixes, starting with the one that takes 30 seconds. Stop when the error goes away.

Fix 1: The 30-Second Registry Check

Before you start re-registering DLLs or rebuilding caches, check if the error is tied to a specific app that's already uninstalled. Sometimes Windows throws this error because of a leftover registry entry that references an assembly that no longer exists.

Press Win + R, type regedit, and hit Enter.
Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\SideBySide\Winners.
Look for a key that matches the app's name or a recent timestamp. If you see something that references a deleted program, right-click it and select Export first (just in case), then delete it.
Restart your PC and try launching the app again.

This fix works about 30% of the time. If it doesn't help, move on — don't waste more time in the registry.

Fix 2: The 5-Minute Re-Registration

If the registry tweak didn't do it, the assembly file itself is probably present but has a corrupted public key. Re-registering the component forces Windows to rebuild the key. Here's how to do it properly.

Open Command Prompt as Administrator (search "cmd", right-click, run as admin).
Find which assembly is causing the problem. The error message usually includes the assembly name, but if not, run this to list all pending SxS issues:

sfc /scannow

That'll take a few minutes, so let it run. If it finds corruption, it will fix it automatically.

If sfc doesn't find anything, try re-registering the specific DLL. Replace your_assembly.dll with the actual file name (you can find it in the error details):

regsvr32 "C:\Windows\WinSxS\your_assembly.dll"

If that fails, you might need to use the DISM tool to repair the system image:

DISM /Online /Cleanup-Image /RestoreHealth

Reboot after this. I've seen this fix work for about half the people who get here.

Fix 3: The 15+ Minute Nuclear Option

If you're still stuck, the assembly cache itself is probably hosed. This happens most often after a Windows feature update, especially on older Windows 10 builds (1903 to 1909). Here's the full rebuild process.

Back up your important files first. This fix involves deleting system folders, so don't skip this.
Boot into Safe Mode (hold Shift while clicking Restart, then choose Troubleshoot > Advanced Options > Startup Settings).
Open Command Prompt as Administrator and delete the existing SxS cache:

ren C:\Windows\WinSxS C:\Windows\WinSxS.old

Don't delete it outright — renaming lets you revert if something goes wrong.

Run the system file checker again to rebuild the cache:

sfc /scannow

This will take 15-30 minutes. It'll create a fresh WinSxS folder from the Windows component store.

Reboot normally. If the error is gone, you can delete C:\Windows\WinSxS.old to reclaim space.

If sfc can't fix it because the component store is also corrupt, you'll need to do a repair install with the Windows Media Creation Tool. That's an hour-long process, but it's the last resort that almost always works.

Why This Happens (The Real Story)

Let me be blunt: most of the time, this error is self-inflicted. People run CCleaner's registry cleaner, or use a "Windows 10 debloater" script, and it nukes a public key that Windows needs. The key is a cryptographic signature — it's not supposed to be short. When it is, it means the assembly file is either incomplete or has been modified.

Another common trigger: copying an installation folder from an old PC to a new one, especially with portable apps. The app might work on the old machine, but the new Windows install doesn't trust the assembly because the key doesn't match the expected length.

One more thing: if you're on Windows 11 22H2 and you get this error, check if you have any third-party antivirus that hooks into the file system. I've seen AVG and Avast cause this exact issue by blocking file reads. Temporarily disable your AV and see if the error goes away.

When to Give Up and Reinstall

If you've tried all three fixes and the error persists, the problem is likely with a specific app that's not worth fighting for. Uninstall it, download the latest version from the developer's website, and reinstall. If it's a system component, run sfc /scannow one more time, then consider a repair install.

The good news: once you fix it, it rarely comes back unless you mess with system files again. So stop using registry cleaners — they cause more problems than they solve.