Fix NS_E_WMP_MMS_NOT_SUPPORTED (0XC00D11BD) in Win Media Player

1. The URL or stream doesn't actually support MMS anymore

I know this error is infuriating — you click a link, Windows Media Player opens, and boom — NS_E_WMP_MMS_NOT_SUPPORTED. Nine times out of ten, the problem isn't your player. It's that the URL you're using is stale or the streaming server stopped supporting MMS years ago. Most media servers moved to HTTP-based streaming (like RTMP or HLS) around 2015. If you're pulling an old bookmark or a link from a forum post from 2008, it's probably dead.

The real fix? Try replacing mms:// with http:// in the URL. For example, if the link is mms://example.com/stream.wmv, change it to http://example.com/stream.wmv. Windows Media Player can handle HTTP streaming just fine on Windows 10 and 11 (build 1909 and later). If that doesn't work, the server itself might be down or the stream is gone entirely. Test the URL in VLC Media Player — it's more forgiving and will tell you if the stream exists at all.

Quick note: The error code 0XC00D11BD specifically means the MMS protocol is either not installed or blocked. On a clean Windows 10/11 install, WMP still ships with MMS support, but it's often disabled by group policies in corporate environments. If you're on a work machine, you might need admin rights to enable it.

2. Missing or corrupted codecs for WMV and ASF files

This tripped me up the first time too. MMS streams typically deliver Windows Media Video (WMV) or ASF (Advanced Systems Format) files. If your Windows Media Player can't decode the stream, it throws the protocol error as a red herring. The real culprit is a missing codec from the Windows Media Format runtime. On Windows 10 version 1809 and earlier, the codecs were bundled. On Windows 11 22H2, they're optional features.

Here's the fix: Go to Settings > Apps > Optional features. Click Add a feature, search for Windows Media Player Legacy, and install it if it's missing. Yes, Microsoft removed the classic WMP from newer Windows builds, but the legacy version still works and includes the MMS protocol stack. After installing, restart WMP and try the stream again.

If you already have that installed, try resetting the codec cache. Open an elevated Command Prompt (right-click Start > Command Prompt (Admin) or Terminal (Admin)) and run:

regsvr32 wmvcore.dll
regsvr32 wmp.dll
regsvr32 wmnetmgr.dll

These commands re-register the core Windows Media components. I've seen this fix the error on Windows 10 Pro 21H2 after a Windows Update broke codec registration. Reboot afterward, then test the URL.

3. Firewall or proxy blocking the MMS protocol

MMS uses port 1755 (TCP and UDP). Many corporate firewalls or home routers block this port by default because it's rarely used anymore. Windows Defender Firewall on Windows 11 also has a default rule that blocks incoming MMS traffic, even though the error is outgoing. Check your firewall rules: Open Windows Security > Firewall & network protection > Advanced settings. Look for inbound rules that reference Windows Media Player or Windows Media Services. If they're blocking, disable them temporarily to test.

If you're behind a proxy (common in offices or schools), MMS traffic might not route through it at all. Try adding an exception in Internet Options: Open Control Panel > Internet Options > Connections tab > LAN settings. Under Proxy server, click Advanced and add *.wmp;*.mms to the Exceptions list. This tells Windows to bypass the proxy for media streams. On Windows 11, you might need to do this in the new Settings app under Network & internet > Proxy.

I've also seen routers with SIP ALG or SPI settings that interfere with MMS. If you're on a home network, log into your router (often at 192.168.1.1 or 192.168.0.1) and disable any ALG (Application Layer Gateway) for Windows Media or RTSP. Reboot the router, then try the stream again.

Quick-reference summary table

If none of these fix it, the stream itself is almost certainly dead. MMS was deprecated by Microsoft in Windows 10, and most internet radio stations and live streams moved on years ago. Your best bet is to find an alternative source (like an MP3 or HLS stream) or use VLC Media Player, which handles MMS via a separate library and is more forgiving. I keep VLC installed on every machine I touch for exactly this reason.