Fix 0x000036B7 Side-by-Side Key Not Found

Windows can't find a needed lookup key in its activation context. Usually caused by broken Visual C++ or .NET installs. Fix: repair or reinstall the runtime.

Quick answer

Repair or reinstall the Visual C++ Redistributables and .NET Framework — 9 times out of 10 that clears 0x000036B7. If it doesn't, use the SxS trace tool to pinpoint the exact manifest and DLL failing.

What's happening under the hood? Windows uses something called an activation context to keep DLL versions from stepping on each other. When an app starts, it reads a manifest file that tells Windows which side-by-side assemblies (like Visual C++ runtime DLLs) it needs. The error ERROR_SXS_KEY_NOT_FOUND means Windows went looking for a specific lookup key inside that context and came up empty. That key is usually tied to an assembly reference that's either missing, corrupt, or pointing at a version that isn't installed. I've seen it most often after a Windows feature update nukes a Visual C++ install, or when someone uninstalled an old runtime and an app still needed it. Had a client last month whose accounting software threw this right after they cleaned out “old programs” — killed the whole print queue because the app couldn't even load.

Fix steps (in order)

Check the Windows Event Log for the exact app and module. Open Event Viewer (eventvwr.msc), go to Windows Logs → Application, and look for an Error event that references the SxS or SideBySide source. It'll tell you the exact assembly name and version it couldn't find. Write it down — you'll need it.
Repair the Visual C++ Redistributables. Go to Control Panel → Programs and Features, find every “Microsoft Visual C++ 2015-2022 Redistributable” entry. Right-click and choose Change → Repair. Do this for each one (x86 and x64). If you're on a 64-bit system, you need both.
Repair the .NET Framework. Download the .NET Framework Repair Tool from Microsoft (it's a standalone utility). Run it, let it scan and fix. This covers .NET 3.5 and 4.x in one go.
Reboot and test the app that failed. If no error, done. If it still pops, move to the alternative fixes.

Alternative fixes when the main one fails

Reinstall the specific runtime from the error. If the event log said it was missing Microsoft.VC90.CRT (that's Visual C++ 2008), grab the correct redistributable from Microsoft's download center. Old versions aren't always in Programs and Features, so you might need to install them fresh.
Use the SxS trace tool for a deep dive. Download the Windows SDK (just the Debugging Tools part is enough) and run sxs.exe trace from an elevated command prompt. It logs every activation attempt. Launch your app, then stop the trace. Look for lines that say ERROR_KEY_NOT_FOUND — that pinpoints the exact manifest entry that's broken. Sometimes it's a third-party DLL in the app folder that references an assembly you've never heard of.
Force a clean reinstall of the app. Uninstall the program completely (use Revo Uninstaller if you want to be thorough), then delete any leftover folders in Program Files and %AppData%. Reinstall as administrator. This clears any stale activation context cache entries.
If it's a system DLL issue, run DISM and SFC. Open an elevated Command Prompt and run DISM /Online /Cleanup-Image /RestoreHealth, then sfc /scannow. This fixes corrupted system files that might be breaking the activation context store.

Prevention tip

Stop uninstalling Visual C++ redistributables just because you think they're junk. They're not. They're shared system components, and each app might need a different version. The safe move: never manually uninstall them. Let Windows updates handle them. Also, keep the .NET Framework repair tool bookmarked — you'll use it again. If you're managing multiple machines, create a script that repairs all VC++ runs in one go using wmic product where "name like '%Visual C++%'" call repair. Saves you from clicking through 20 dialogs.