Fix NS_E_PROXY_SOURCE_ACCESSDENIED (0xC00D2EF7) in Windows Media Player

What 0xC00D2EF7 actually means

You're watching a video on a media server — maybe a home NAS running Plex or a corporate streaming box — and Windows Media Player throws NS_E_PROXY_SOURCE_ACCESSDENIED. The message is vague, but the meaning is narrow: WMP asked your proxy to forward a request to the media server, and the proxy said no because it didn't have valid credentials.

This isn't a codec problem. It isn't a firewall problem. It's an authentication delegation problem, and it shows up most often on corporate laptops where a proxy is configured by group policy but Windows Media Player wasn't given the right credentials to pass through it.

Cause 1: Proxy is enabled but local addresses aren't bypassed

This is the most common trigger by far. You're on a work laptop, connected to the corporate network via VPN, and your proxy settings include a checkbox for Bypass proxy server for local addresses that's unchecked. Your media server has an internal IP like 192.168.1.50, but Windows Media Player still routes the request through the proxy — which has no business handling internal traffic and rejects it with 0xC00D2EF7.

The real fix is to add your media server's IP range to the bypass list.

1. Press Win + R, type inetcpl.cpl, and hit Enter. The Internet Properties window opens.
2. Click the Connections tab. You should see three buttons near the bottom: Setup, LAN settings, and Dial-up and Virtual Private Network settings.
3. Click LAN settings. A smaller window opens showing your proxy configuration.
4. If Use a proxy server for your LAN is checked, look directly below it for Bypass proxy server for local addresses. Check that box if it isn't already.
5. Now click Advanced in the same window. In the Exceptions box, add your media server's address. For a machine at 192.168.1.50, you'd type:

   192.168.1.50;192.168.*.*;*.local;10.*.*.*

6. Click OK on the Advanced window. Click OK on the LAN Settings window. Click OK on Internet Properties.
7. Close Windows Media Player completely — check the system tray, it likes to hide there. Reopen it and try streaming again.

After clicking OK on the last window, you should see Internet Properties close without errors. If you get a UAC prompt, that's normal — click Yes. When you relaunch WMP and hit play, the stream should start within a few seconds. If you still get 0xC00D2EF7, move to the next cause.

Cause 2: Stored proxy credentials are wrong or missing

Windows caches proxy credentials in Credential Manager. If someone changed your domain password, or IT pushed a new proxy server that requires different credentials, the old cached ones get sent — and the proxy rejects them silently, passing 0xC00D2EF7 back to Windows Media Player.

Here's how to clear and re-enter them:

1. Open the Start menu and type Credential Manager. Click the matching result.
2. Click Windows Credentials.
3. Scroll through the list. Look for entries labeled with your proxy server's hostname, or generic entries like MicrosoftAccount:target=SSO_POP_Device or anything containing proxy.
4. Click the arrow next to each suspicious entry and choose Remove. Confirm when prompted.
5. Do the same under Generic Credentials if you see anything matching your proxy hostname.
6. Restart Windows Media Player. When it tries to stream through the proxy again, Windows should prompt you for fresh credentials. Enter your current domain username and password.

If Windows doesn't prompt and you still get the error, the proxy might be using NTLM authentication, which WMP handles poorly. In that case you'll need to configure the proxy to accept your Windows logon automatically. That's a server-side setting — talk to whoever manages the proxy.

Cause 3: Network discovery and file sharing are disabled

This one trips people up because it doesn't look related to proxy authentication. But when Windows can't discover the media server on the local network, it falls back to routing everything through the default gateway — which happens to be your corporate proxy. Disable network discovery and you've effectively forced WMP to try proxy authentication for a server it should be talking to directly.

Turn discovery back on:

1. Click the network icon in the system tray (bottom right of your screen).
2. Click Network & Internet settings. The Settings app opens to the Status page.
3. Click Network and Sharing Center (or Properties if you're on Windows 11 — the layout changed).
4. Click Change advanced sharing settings on the left side.
5. Expand Private and make sure Turn on network discovery and Turn on file and printer sharing are both selected.
6. Expand Guest or Public and set network discovery to On there too, unless you're on public Wi-Fi.
7. Click Save changes. You'll need admin rights — if you don't have them, this step will fail with a UAC prompt you can't satisfy.
8. Reboot. Seriously, reboot. Windows doesn't always apply discovery changes without one.

After the reboot, you should see your media server listed under Network in File Explorer. If you can browse to it there, Windows Media Player will be able to stream from it directly, bypassing the proxy entirely.

One thing to skip

Don't bother reinstalling Windows Media Player or running sfc /scannow. This error is never caused by corrupt system files. You'd just be wasting twenty minutes staring at a progress bar.

Quick reference

Start with the bypass list. That one fix resolves the majority of 0xC00D2EF7 cases because corporate proxies are almost never supposed to handle LAN traffic. If you're still stuck after all three, get the proxy logs from your IT team — they'll show exactly which credentials were rejected and why.