Fix WMP Error 0XC00D115C NS_E_WMP_CONVERT_PLUGIN_UNAVAILABLE

You're trying to add a media file to Windows Media Player, and instead of the song or video showing up, you get a popup with error 0XC00D115C — Windows Media Player cannot add the file to the library. Annoying as hell, I know. Let's cut through the noise and fix it.

What causes error 0XC00D115C?

This error means WMP can't find or load a specific plugin it needs to convert that file format — usually something like an FLAC, OGG, or a weirdly encoded MP4. The plugin path in the registry is either missing, pointing to a file that doesn't exist, or got corrupted after a Windows update or a codec pack install (looking at you, K-Lite). I've seen this most often after upgrading from Windows 10 to 11, or after uninstalling a third-party media player that took the shared codec with it.

The fix: Restore the missing registry key

We're going to edit the Windows Media Player registry key to point to the correct plugin folder. You'll need admin rights on your PC.

Press Windows Key + R, type regedit, and hit Enter. If UAC asks, click Yes.

Go to this path (copy and paste it into the address bar in Regedit):

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MediaPlayer\Setup\User Interface

Look on the right for a string value named PluginDir. If it's missing, skip to step 5.
If PluginDir exists, double-click it. The Value data should be something like:
```
C:\Program Files\Windows Media Player\Plugins
```
If it's different or empty, change it to that exact path. Click OK.
If the value wasn't there, you need to create it: right-click in the empty space on the right, select New → String Value, name it PluginDir, then double-click it and set the data to:
```
C:\Program Files\Windows Media Player\Plugins
```
Close Regedit.
Open Windows Media Player, try to add the file again (drag it in or use File → Add to Library).

After step 7: If the error still appears, you might be missing the actual plugin files. Let's check that next.

Verify the plugin folder exists

Open File Explorer and go to C:\Program Files\Windows Media Player.
Look for a folder named Plugins. If it's not there, create it.
Inside that folder, you should see files like wmp.dll, npwmp.dll, and a few others. If the folder's empty or missing these, you'll need to repair Windows Media Player.

If the plugin folder is empty or missing

Go to Settings → Apps → Optional features. Find Media Features (or Windows Media Player on older builds). Uncheck it, restart your PC, then go back and recheck it. This reinstalls WMP and its plugins. I've had to do this twice on a Dell laptop running Windows 11 22H2 — worked like a charm.

Why this works

WMP uses plugins to decode non-Microsoft formats. The registry tells it where those plugins live. If that path is wrong, WMP doesn't even try to load them — it throws the 0XC00D115C error instead. By resetting the PluginDir to the default, you're giving WMP the map to its own toolbox. No map, no tools, no library.

Less common variations of the same problem

Sometimes the registry path is different. On 64-bit Windows, WMP might look for a separate plugin path under:

HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\MediaPlayer\Setup\User Interface

Check that too. I've seen copies of the key in both places — deleting the wrong one breaks things. Don't delete anything, just check PluginDir there and correct it if needed.

Another variation: after a failed codec pack install, the PluginDir value points to a custom folder that no longer exists, like C:\Program Files (x86)\CodecPack\Plugins. WMP tries to load plugins from there, finds nothing, errors out. Same fix — point it back to the default.

One more oddball: if you're using a portable version of WMP or a third-party skin, the error can show up even with the correct registry. In that case, switch back to the default WMP skin first, then try the fix.

How to prevent this from happening again

Don't install random codec packs. I know it's tempting to grab that one pack that promises to play everything, but they often overwrite WMP's plugin registration. Stick with what Windows provides, or use a modern player like VLC for your weird files. If you must install codecs, use the official Microsoft codec pack from the Store — it won't mess with the registry.

Also, when you uninstall a third-party media player, check for remnants. Some uninstallers leave old plugin references behind. After uninstalling, open Regedit and look at both the paths above — if PluginDir points to a folder that doesn't exist, fix it immediately.

Finally, before any major Windows update, take a screenshot or export the MediaPlayer registry key. That way, if the update breaks it, you can restore it in two seconds. A little housekeeping saves a lot of headaches.