NS_E_CHANGING_PROXY_PROTOCOL_NOT_FOUND 0xC00D10C4 Fix

Quick answer

Delete the proxy registry key for Windows Media Player: run reg delete HKCU\Software\Microsoft\MediaPlayer\Proxy /f and restart the player.

Why this happens

You're streaming a video from a DLNA server — maybe a Synology NAS running Media Server, or a Plex instance on a Raspberry Pi — and halfway through the playback, Windows Media Player throws NS_E_CHANGING_PROXY_PROTOCOL_NOT_FOUND (0xC00D10C4). The player can't find the proxy protocol it was told to use. What's actually happening here is that Windows Media Player caches proxy settings in HKEY_CURRENT_USER\Software\Microsoft\MediaPlayer\Proxy. When the media server changes its protocol (e.g., from HTTP to RTSP mid-stream, or when the network topology shifts), the cached proxy entry doesn't match the server's actual protocol. The player doesn't gracefully fall back — it bails with this error.

I've seen this most often when you have multiple network adapters (WiFi and Ethernet) or when a VPN kicks in and changes your routing. The player's proxy config gets stale. The fix is straightforward: clear that cache.

Fix steps

1. Close Windows Media Player entirely. Make sure it's not running in the background — check Task Manager if you're paranoid.
2. Open a Command Prompt as Administrator. Press Win+R, type cmd, then Ctrl+Shift+Enter.
3. Delete the Media Player proxy registry key. Run this command:

   reg delete HKCU\Software\Microsoft\MediaPlayer\Proxy /f

   The /f flag forces deletion without confirmation. This removes the entire Proxy subtree.
4. Restart Windows Media Player and try streaming again. The player will rebuild the proxy key fresh from the server's current protocol.

That's the fix. But here's the nuance: if you're on a corporate network with a manual proxy setup (like a proxy.pac file), you might need to re-enter those proxy settings after the deletion. The player defaults to Auto-detect proxy settings after the key is gone.

Alternative fixes if step 3 fails

1. Reset Windows Media Player settings completely. Open Windows Media Player, press Alt to show the menu bar, go to Tools > Options > Player tab, and click Restore defaults. This also nukes the proxy cache but wipes other preferences too.
2. Disable the proxy manually via Group Policy. For Windows 10 Pro/Enterprise only: run gpedit.msc, navigate to User Configuration > Administrative Templates > Windows Components > Windows Media Player > Networking, and set Configure Proxy Settings to Disabled. This prevents the player from caching any proxy protocol.
3. Switch to a different media player. VLC doesn't suffer from this bug because it doesn't cache proxy protocols. If you're tired of fighting WMP, use VLC for DLNA streaming — it's more reliable.

Prevention tip

To keep this from recurring, set Windows Media Player to Auto-detect proxy settings permanently. Go to Tools > Options > Network, select the protocol you're using (usually HTTP or RTSP), and click Configure. Choose Autodetect proxy settings instead of Use proxy settings from the browser or a manual config. This way, the player renegotiates the protocol every time it connects, avoiding stale cache entries.

If you run a media server like Plex or Jellyfin, keep its protocol setting consistent — don't let it auto-switch between HTTP and HTTPS mid-stream. That mismatch is the trigger for this error.