That error is annoying, but here's the fix
You're staring at NS_E_INVALID_INDEX2 (0XC00D00D9) and it's blocking your media playback. I've seen this on a client's old HP laptop—they thought their music collection was corrupt. It's not. The index in Windows Media Player's library is stale or broken. Reset it and you're back in business.
Fix: Reset WMP Library and Clear Cache
- Close Windows Media Player (or whatever app threw the error).
- Delete the library database files. Press Win+R, type
%LOCALAPPDATA%\Microsoft\Media Player, and hit Enter. You'll see files likeCurrentDatabase_372.wmdbandLocalMLS.wmdb. Select them all and press Delete. Don't worry—WMP rebuilds them from scratch. - Clear thumbnail cache. In the same folder, look for a subfolder
Thumbnails—delete everything inside it too. This forces WMP to re-scan media metadata. - Restart Windows Media Player. It'll prompt you to re-add your music/video folders. Point it to your libraries and let it rescan.
That's the core fix. Takes 2 minutes, and I've used it on Windows 7, 10, and 11 with identical results.
Why this works
The error code 0XC00D00D9 means the media library's internal index points to something that isn't there—like a file that was moved, renamed, or deleted since the last scan. WMP builds that index when it first catalogs your folders. When the index gets out of sync, any operation that references it (playing a file, browsing the library) fails with NS_E_INVALID_INDEX2.
Deleting the .wmdb files forces WMP to rebuild the index from the actual files on disk. It's like clearing a corrupted database. I had a client last month whose entire print queue died because of a similar index issue in the spooler—same principle, different subsystem.
Quick alternative: Reset via Settings
If you're on Windows 10 or 11, you can also do this through Settings. Go to Apps > Apps & features, find Windows Media Player, click Advanced options, then Reset. That does the same thing but also resets app preferences. Use that if the manual file delete feels risky.
Less common variations
Sometimes the error isn't from WMP itself but from a third-party app that uses Windows Media Player's components—like older media servers or video editing tools. In those cases:
- Check for pending updates. If the app is outdated, it may reference an index format that's changed. Update the app or Windows Media Player via Windows Update.
- Run the Windows Media Player setup repair. Go to Control Panel > Programs > Turn Windows features on or off. Uncheck Media Features, restart, then re-check it. This re-registers the WMP DLLs that handle indexing.
- If you're using a network drive, the index might be pointing to a mapped drive that isn't connected. Reconnect the drive and rescan. I've seen this with a NAS that had a sleep timer—the drive disconnected, and the index went stale.
When it's not the index at all
Rare case: a corrupt media file itself can trigger this error. If the fix above doesn't work, try playing the file directly via File Explorer. If it plays fine, the index is the issue. If it errors, the file is corrupt—re-download or re-rip it.
Prevention
This error comes back if you let your media folders get messy. Keep your files in one place and don't move them mid-scan. If you're using a NAS or external drive, make sure it's always on before launching WMP. Also, run a quick library rebuild every few months—go to Manage Libraries in WMP, remove and re-add your music folder. That keeps the index fresh without waiting for an error to force the fix.
One more thing: if you're a hoarder like me and have 50,000 tracks, the index can corrupt more often. Set WMP to monitor folders automatically (it does by default) but don't let it run while you're copying large batches of files. Copy first, then let it scan.