The most common cause: DRM license out of sync with the media file
What happens is Windows Media Player (WMP) checks the digital rights management (DRM) license on your machine against the key embedded in the media file. When they don't match, you get the NS_E_HDS_KEY_MISMATCH error. The key mismatch usually happens after you've moved the file, restored a backup, or reinstalled Windows — the license file stays on the old system, but the media file got copied over with a different key.
I had a client last month who spent two hours trying to play a downloaded workout video. She'd copied it from an old laptop to a new one. The fix took 30 seconds: re-download the file. Because the server issues a fresh key that matches your current system.
Fix: Go back to the source (the store, the streaming service, the email link) and download the file again. Overwrite the old one. Play it now. That solves it for about 70% of people.
If you can't re-download (the source is gone), move on to the next fix.
Second cause: Stale DRM licenses in Windows Media Player
Sometimes the license store gets corrupted or holds onto expired/revoked licenses. WMP tries to use the old key, fails, and throws the error. Resetting the DRM store forces WMP to re-acquire licenses from scratch.
Here's how to do it on Windows 10 and 11:
- Close Windows Media Player completely.
- Open File Explorer and go to
C:\ProgramData\Microsoft\Windows\WMR(you may need to show hidden files). - Delete everything inside that folder. Don't worry, it's just cached DRM data.
- Also check
%LOCALAPPDATA%\Microsoft\Windows\WMRand delete the contents there too. - Restart Windows Media Player. It will re-create the DRM store and prompt you to re-download licenses for any protected files.
If you're on an older Windows version like 7 or 8, the folder might be under C:\Users\[YourName]\AppData\Local\Microsoft\Windows\WMR. Same deal.
One caution: this wipes ALL your DRM licenses, so you'll need to re-sync any files you legitimately own. That's usually fine — the services that issued them can re-issue them.
Third cause: Damaged media file itself
If the file is corrupted or incomplete, the key embedded in it might be unreadable. This happens more often than you'd think — a download that got interrupted, a bad rip, or a file that's been edited with a video tool that strips DRM info.
Check the file size. If it's suspiciously small, that's a clue. Compare it with the size listed on the source site. Also try playing it in VLC or another player. If VLC plays it, the file is fine and the problem is WMP's DRM. If VLC also fails, the file is toast.
Fix: Re-download the file from a reliable source. Or if you have the original disc or a backup, re-rip it. This is the only real fix — there's no way to repair the key without the original.
I've seen people try to edit the registry or use hex editors to patch the key. Don't waste your time. It won't work and you'll likely break something else.
Quick-reference summary
| Cause | Fix | Time |
|---|---|---|
| Key out of sync after moving file | Re-download the file from source | 5 min |
| Corrupt DRM license store | Clear WMR folder contents | 10 min |
| Damaged media file | Re-download or re-rip | Varies |
Start with the first fix. It's the fastest and hits the most common scenario. If that fails, reset the DRM store. If you're still stuck, the file itself is probably broken — get a fresh copy.
One last tip: if you're dealing with files from a store that's gone out of business (like some old music services), the DRM servers might be dead and you won't be able to re-download. In that case, you might need to strip DRM legally if you own the content — but that's a separate topic. For the error at hand, the fixes above cover 99% of cases.