SXS Duplicate IID 0x36C8: What It Is and How to Fix It

You're trying to launch a program—maybe an old business app, a game with a custom launcher, or a freshly installed utility—and instead of the window, you get a dialog box that says ERROR_SXS_DUPLICATE_IID with code 0X000036C8. This typically pops up right after you've installed a Windows update, run a third-party DLL registration script, or installed a piece of software that bundles its own copy of a common runtime like VC++ redistributable or .NET. The trigger is almost always a recent change to the system's side-by-side assembly store, not a hardware issue or a corrupted download.

What's actually happening here is that the Windows Side-by-Side (SxS) mechanism—the thing that manages DLL versions so different apps can use different versions of the same library—has discovered two different assemblies claiming the same COM Interface Identifier (IID). COM interfaces are identified by a globally unique GUID, and the system assumes that each IID belongs to exactly one implementation. When two assemblies in the WinSxS store register the same IID, the loader throws this error because it can't decide which one is the "real" implementation. It's not a permission problem, not a missing file, and not malware. It's a conflict in the manifest database.

The reason this happens after an update is that Windows Update sometimes installs a new version of a system assembly while an older version is still referenced by an application manifest. The older assembly is still in the store, but the new one has a revised manifest that also lists the same IID. The system doesn't merge them; it just reports the duplication. Similarly, a poorly written installer that manually re-registers a COM DLL with regsvr32 can overwrite the registration that the SxS store already has, causing a duplicate entry in the registry's Interface key.

Here's the fix. You'll need to clean out the conflicting entries and then rebuild the SxS store. This isn't destructive to your personal files, but it does require administrative rights and a restart.

1. Identify the offending assembly. Open Event Viewer (eventvwr.msc) and look under Windows Logs > Application for the most recent SxS source event. It usually includes the assembly name and the IID. Write those down—you'll need them if the generic fix doesn't work.
2. Clear the SxS store cache. Open an elevated Command Prompt (right-click Command Prompt, Run as administrator). Run the built-in deployment image servicing command:

DISM /Online /Cleanup-Image /StartComponentCleanup

This removes superseded versions of side-by-side assemblies. It's safe because any assembly that's still referenced by an installed app will be left alone. The command can take 10 to 20 minutes, so let it run.

3. After the cleanup completes, reboot. The WinSxS store is rebuilt on startup, and the duplicate IID entries get consolidated. If the error appears on a specific app, try launching it again now.
4. If the error persists, re-register the affected COM component. Open an elevated Command Prompt and run the following, replacing YourApp.dll with the DLL name from the Event Viewer:

regsvr32 /u YourApp.dll
regsvr32 YourApp.dll

This forces a clean registration. Note that this only works if the DLL is a classic COM server, not a WinRT component. If it's a WinRT component, skip this step—it won't help.

5. If the app still won't start, remove the duplicate registry key. Open regedit and go to HKEY_CLASSES_ROOT\Interface. Look for a key with the same IID value as in the event log. If there are two keys with the same GUID but different class registrations under HKEY_CLASSES_ROOT\CLSID, you need to figure out which one is the older version. This is the delicate part—deleting the wrong key can break other apps. Back up the entire Interface key first by right-clicking and choosing Export. Then delete only the key that corresponds to the older assembly (check the modified date). Reboot.

If it still fails after all that, you're dealing with a deeper system file corruption. Run the System File Checker in an elevated Command Prompt:

sfc /scannow

If SFC finds and repairs files, reboot and try the app again. If SFC turns up nothing, the last resort is an in-place repair install of Windows 10 or 11. That preserves your files and apps but replaces the system files. It's a heavy step but it clears any lingering manifest conflicts that even the DISM cleanup missed.

One thing worth noting: if this error only appears on one machine in your office and not another, check whether the machines have different Windows update levels. A machine that's behind on updates might still have the old assembly version, while one that's fully patched has the new one. The fix is to bring both machines to the same patch level—that's often the real culprit in enterprise environments.