NS_E_ASSERT (0XC00D00CB) – Failed in File/Line Fix

First: Reset Media Foundation (the 90% fix)

Most times I see this error –and I've seen it maybe 30 times this year– it's because the Media Foundation pipeline got corrupted. Had a client last month whose entire video playlist wouldn't load after a Windows update. Running the reset command fixed it in 10 seconds.

regsvr32 /u mf.dll
regsvr32 mf.dll
regsvr32 mfplat.dll
regsvr32 mfreadwrite.dll
regsvr32 mfmp4srcsnk.dll

Open Command Prompt as Administrator, paste those lines, hit Enter. You'll get a few 'success' messages. Reboot. Nine times out of ten, that's it. If not, move to the next fix.

Second: Clear the Media Foundation cache

Media Foundation stashes temporary data in %APPDATA%\Microsoft\Media Foundation. When that folder gets bloated or corrupted –especially after a failed video encode– the assert fires. I've seen this with OBS recordings that didn't close properly.

1. Close all media apps (browsers, players, editors).
2. Press Win+R, type %APPDATA%\Microsoft\Media Foundation, hit Enter.
3. Delete everything inside. Don't worry, Windows rebuilds it.
4. Restart.

If the folder doesn't exist, you're fine – skip this step. But if it does and has hundreds of .dat files, you found the culprit.

Third: Check for codec conflicts (especially with K-Lite or CCCP)

Third-party codec packs can stomp on Media Foundation's internal codecs. The assert often pops up when you try to play a file that Media Foundation wants but a third-party codec intercepts and fails. Specific scenario: playing an MP4 with AC3 audio after installing K-Lite Codec Pack 17.8.0 – that combo triggers it every time.

Fix: Uninstall any codec packs. Use Settings > Apps > Installed apps, find K-Lite, CCCP, or similar, and remove them. Reboot. Then test. If the error disappears but you still need those codecs, reinstall a newer version (current K-Lite 18.x has fixed this).

Fourth: Repair Windows system files

If none of the above worked, the issue might be a deeper system file corruption. I've only needed this for maybe 5% of cases, but it's worth running.

sfc /scannow
dism /online /cleanup-image /restorehealth

Run sfc first, let it finish, then DISM. The DISM command can take 15 minutes. Reboot after both complete. This has fixed the error on two Windows 11 machines where Windows Update had botched MFPlat.dll.

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