What causes this error
The error NS_E_CHANGING_PROXY_PORT (0XC00D10C1) pops up when you try to change the proxy port in Windows Media Player, but the proxy type isn't set to "Custom". I see this a lot after Windows updates that reset proxy settings, or when someone's IT department pushes a proxy via Group Policy.
Here's the thing — Windows Media Player has its own proxy settings separate from Internet Explorer's. If the proxy type is "Auto-detect" or "Use browser proxy", you can't change the port directly. The error is just Windows saying "Hey, pick custom first."
Let's fix it. Start with the quickest option and move down if needed.
Quick fix (30 seconds) — Set proxy type to custom
This fixes 9 out of 10 cases. Open Windows Media Player, go to Tools > Options > Network. Under the streaming proxy settings, find the protocol (usually HTTP or RTSP). Select it, click Configure, then choose Custom in the dropdown. Now you can change the port number. Hit OK twice.
If you can't find Tools, press Alt to show the menu bar. If you're on Windows 11, it's still there — just a bit hidden.
Test by playing a streaming URL. If error's gone, you're done. If not, move to the next fix.
Moderate fix (5 minutes) — Reset proxy settings in Registry
Sometimes the proxy type gets stuck even after changing it in the UI. The registry doesn't lie. Open regedit (press Win + R, type regedit). Navigate to:
HKEY_CURRENT_USER\Software\Microsoft\MediaPlayer\Player\ProxyYou'll see subkeys like http, rtsp, mms. For each one, check the Type DWORD value:
- 1 = Use browser proxy (don't change)
- 2 = Auto-detect (don't change)
- 3 = Custom (this lets you change the port)
Set the Type to 3 for the protocol you need. If there's a Port DWORD, set it to whatever port you want (e.g., 8080). Close regedit and restart Windows Media Player.
If you don't see the Proxy key at all, create it manually — right-click on MediaPlayer, choose New > Key, name it Proxy, then add the protocol subkeys.
Advanced fix (15+ minutes) — Group Policy or corrupted profile
If the error still shows up, something else is overriding your settings. Three possible causes here.
Group Policy locking proxy settings
Open gpedit.msc (only on Pro/Enterprise editions). Navigate to Computer Configuration > Administrative Templates > Windows Components > Windows Media Player > Network. Look for "Set HTTP proxy" or similar policies. If they're enabled with a value like "Use browser proxy", that's your problem. Set them to Not Configured or Disabled. You'll need admin rights for this.
If you're on Windows 10/11 Home, check the registry at:
HKLM\SOFTWARE\Policies\Microsoft\WindowsMediaPlayerIf you see keys like EnableHttpProxy or HttpProxyType, delete them or set them to 0.
Corrupted user profile
This is rare but happens. Create a new local user account (Settings > Accounts > Family & other users > Add someone else). Log into that account, open Windows Media Player, try to change the proxy port. If it works, the old profile is busted. Migrate your files and ditch the old profile.
Alternative — Use VLC instead
Honestly, if you're fighting this for more than 15 minutes, just use VLC media player. It doesn't have this proxy nonsense, and it handles streaming way better. Windows Media Player is a dinosaur for network streaming — it uses old protocols like MMS that barely exist anymore.
Prevention tips
Once you fix it, you can avoid it coming back:
- Don't let Windows Update reset your proxy settings. After a feature update, check this registry key again.
- If your company uses proxy auto-config (PAC), you'll never have this problem because PAC is handled at the OS level, not per app.
- Disable Windows Media Player's proxy entirely if you don't need it — set the Type to 0 (no proxy) if your network doesn't require one.
I've seen this error on everything from Windows 7 to Windows 11 23H2. The registry fix always works unless Group Policy is in play. Start with the UI, then regedit, and you'll be streaming again in minutes.