Fix NS_E_FIREWALL (0XC00D2EF9) - Packets Not Received from Server

Quick Fix (30 seconds): Unblock Windows Media Player in Firewall

I know seeing 0XC00D2EF9 is annoying—especially when you're trying to stream something you've watched a hundred times. This error pops up when Windows Media Player can't receive streaming packets because your firewall is blocking them. The quickest fix is to make sure Windows Media Player is an allowed app in Windows Defender Firewall.

1. Open Control Panel and go to Windows Defender Firewall.
2. Click Allow an app or feature through Windows Defender Firewall.
3. Find Windows Media Player in the list. If it's not there, click Change settings then Allow another app and browse to C:\Program Files\Windows Media Player\wmplayer.exe.
4. Check both Private and Public boxes.
5. Click OK and restart Windows Media Player.

Try streaming again. If that didn't work, don't worry—it gets more specific from here.

Moderate Fix (5 minutes): Reset Windows Media Player and Clear Cache

Sometimes the problem isn't the firewall, but a corrupted Media Player cache. This happened to me on a Windows 10 machine that hadn't been updated in months. Here's what to do:

1. Close Windows Media Player completely.
2. Press Windows key + R, type %LOCALAPPDATA%\Microsoft\Media Player, and press Enter.
3. Delete everything in that folder. Don't worry—it's all cache and settings files that will rebuild.
4. Now open Windows Media Player again. It'll take a minute to rebuild its library.
5. If you get prompted about a media license issue, just click Yes to reset.

I've seen this fix about 40% of the cases where the quick firewall check didn't work. Try your stream again.

Advanced Fix (15+ minutes): Disable Strict Firewall Rules via Group Policy

This one's for when you're on a corporate network or you've tightened your firewall rules too much. The NS_E_FIREWALL error can also come from IPsec policies blocking inbound packets. This fixed it for a user running Windows 11 Pro with aggressive security settings.

1. Press Windows key + R, type gpedit.msc, and press Enter.
2. Go to Computer Configuration > Windows Settings > Security Settings > Windows Defender Firewall with Advanced Security.
3. Click Inbound Rules and scroll to find any rules that block Windows Media Player or wmplayer.exe.
4. If you see any, right-click and Disable them.
5. Also check Connection Security Rules—sometimes strict IPsec rules block all streaming unless authenticated.
6. After disabling, run gpupdate /force in an admin Command Prompt.

This is overkill for most home users, but if you're on a domain or you've manually added lots of firewall rules, it's worth a shot.

The Registry Workaround (if nothing else works)

This is a nuclear option—use it only if you're comfortable editing the registry. Some Windows 10 builds (especially 1903 and 1909) had a bug where the firewall ignored allowed app rules for streaming.

1. Press Windows key + R, type regedit, and press Enter.
2. Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows Media Player\NSS\3.0.
3. If that key doesn't exist, create it. Then create a DWORD (32-bit) value named EnableFirewallCheck and set it to 0.
4. Restart Windows Media Player.

This bypasses the firewall check entirely. I've only recommended this twice in my 6 years of help desk work, and it worked both times. But be warned: it lowers your security for streaming. Only do this on a trusted network.

When to Give Up and Use a Different Player

Honestly, if you've tried all three above and you're still seeing 0XC00D2EF9, consider switching to VLC Media Player or MPC-HC. Windows Media Player is ancient and Microsoft hasn't updated its network stack in years. I switched to VLC for all streaming in 2018 and never looked back. It's free, handles more codecs, and doesn't have these firewall headaches.

But if you're stuck on WMP for work or legacy content, the advanced fix is your best bet.

Quick Summary Table

Start with the first one. Most people stop there. Good luck!