Fix NS_E_WMP_CONVERT_PLUGIN_UNKNOWN_FILE_OWNER (0XC00D115E)

This error is maddening — I know

You try to add a music file or video to Windows Media Player, and it just says it can't add it to the library. The error code 0XC00D115E (NS_E_WMP_CONVERT_PLUGIN_UNKNOWN_FILE_OWNER) pops up, and you're left staring at a useless message. I've been there, and the fix is almost always simpler than you think.

The fast fix: take ownership of the file

Windows Media Player's converter plugin throws this error when it can't verify who owns the file — usually because the file was copied from another PC, an external drive, or downloaded from a source that changed the ownership metadata. Here's what actually works:

1. Right-click the file you can't add (or the folder containing it) and choose Properties.
2. Go to the Security tab, then click Advanced.
3. Next to Owner, click Change.
4. In the box that opens, type your Windows username (e.g., YourName if you use a local account, or YourEmail@outlook.com if you use a Microsoft account). Click Check Names to verify it exists, then OK.
5. Check Replace owner on subcontainers and objects if this is a folder.
6. Click OK twice to close everything.

Now try adding the file to Windows Media Player again. 9 out of 10 times, it just works.

Why this works

The WMP converter plugin checks the file's owner SID (Security Identifier) when importing. If the owner is a user account that no longer exists on your machine — like the original PC's user — the plugin throws the UNKNOWN_FILE_OWNER error. Taking ownership reassigns that file to your current account, which WMP trusts. This isn't a driver issue, a codec problem, or a corrupted library — it's literally Windows being paranoid about file provenance.

When the basic fix doesn't do it

I've seen cases where the error happens on an entire folder of music, even after taking ownership. Here's what else to check:

1. The file is read-only (but not really)

Some media files have hidden read-only attributes that block the converter. Open a command prompt as administrator and run:

attrib -r "C:\Path\To\Your\File.mp3" /s /d

Replace the path with your actual file or folder. The /s flag applies it to all subfolders, /d to directories.

2. Windows Media Player library corruption

If ownership is fine but the error persists, the library database might be corrupted. Close WMP, then delete or rename the library folder:

C:\Users\YourUsername\AppData\Local\Microsoft\Media Player

WMP will rebuild it on next launch. You'll lose your playlists, but the files will reimport cleanly.

3. Third-party shell extensions (rare but real)

I once traced this error to a buggy codec pack's shell extension that was hijacking the file open dialog. If you have something like K-Lite Codec Pack or a media converter installed, try disabling its shell extension via ShellExView (free from NirSoft). Or just uninstall the codec pack temporarily to test.

Prevention: keep your files local and owned

This error is most common when you copy files from external drives, network shares, or old backups. To avoid it in the future:

• When transferring music from an old PC, copy the files to a folder on your desktop first, then take ownership of the entire folder before importing to WMP.
• If you download music (legally, of course), save it to a folder you own, not a system folder like Downloads under C:\Users\Default.
• Use a tool like takeown from an admin command prompt on entire media directories after a big transfer:

takeown /f "D:\Music" /r /d y

That command recursively takes ownership of everything inside D:\Music without asking for each file. Pair it with icacls to grant full control:

icacls "D:\Music" /grant "%USERNAME%":F /t

Do that once after a big import, and you'll never see 0XC00D115E again.

I've been running a help desk blog for years, and this error fooled me the first time too. But now you know the trick — it's almost never the file itself, just who owns it. Take ownership, add to library, done.