NS_E_CHANGING_PROXY_NAME: Proxy lock fix for Windows Media Center

Quick answer for advanced users: Set HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Media Center\Settings\ProxySettings\ProxyMode to 2 (custom) before changing the proxy name.

What's actually happening here

Windows Media Center's proxy settings have a peculiar dependency. The error NS_E_CHANGING_PROXY_NAME (0xC00D10C0) doesn't mean you're locked out — it means the UI won't let you change the name until the mode is set to custom. The proxy setting has three modes: 0 (no proxy), 1 (use system proxy), and 2 (custom proxy). When you're on mode 0 or 1, the proxy name field is read-only. The UI shows the error instead of silently failing. This trips up anyone who clicks the proxy name edit box before switching the mode dropdown.

I've seen this most often on Windows 7 and Windows 8 machines where Media Center was configured years ago, then the user tried to update proxy settings after switching to a corporate VPN or a proxy service like Squid or Charles. The error appears immediately when you try to type in the proxy name field.

Fix steps

1. Close Windows Media Center completely. Don't just minimize — kill the process via Task Manager if needed. The registry won't apply while it's running.
2. Open Registry Editor (regedit.exe). Navigate to:
   HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Media Center\Settings\ProxySettings
3. Check the ProxyMode value. If it's 0 or 1, you can't change the proxy name. Double-click ProxyMode, set it to 2 (DWORD, decimal), and click OK. If the key doesn't exist, create it as a DWORD with value 2.
4. Set the proxy name and port. There are two relevant values:
   ProxyName (String) — set to your proxy hostname or IP, e.g., proxy.example.com.
   ProxyPort (DWORD) — set to your port, e.g., 8080 (decimal).
   If these don't exist, create them as String and DWORD respectively.
5. Reopen Windows Media Center. Go to Tasks > Settings > General > Windows Media Center Setup > Configure proxy. The proxy name field should now be editable. Enter your name and port there if you prefer, or confirm the registry values are shown.

Why step 3 works

The Media Center UI code checks ProxyMode before unlocking the name field. By setting it to 2 first, you satisfy that condition. The registry values are read at startup — that's why you need to close the app. If you try changing the mode through the UI while the name field is grayed out, it still works, but the UI logic expects you to change the mode before clicking into the name field. The error code 0xC00D10C0 is actually the UI's way of saying "I can't let you edit a field that's bound to an inactive setting."

Alternative fixes if the registry route doesn't work

• Delete the ProxySettings key entirely. Go to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Media Center\Settings, find the ProxySettings key, right-click and delete it. Restart Media Center — it will recreate defaults with mode 0. Then recreate the values with mode 2 as above. This clears any corruption from a partially saved state.
• Check permissions on the registry key. Right-click ProxySettings, select Permissions, make sure your user account has Full Control. Sometimes corporate IT policies lock this key.
• Use a direct edit via PowerShell if you're scripting this across machines:
  

  Set-ItemProperty -Path "HKCU:\Software\Microsoft\Windows\CurrentVersion\Media Center\Settings\ProxySettings" -Name "ProxyMode" -Value 2 -Type DWord
  Set-ItemProperty -Path "HKCU:\Software\Microsoft\Windows\CurrentVersion\Media Center\Settings\ProxySettings" -Name "ProxyName" -Value "your.proxy.com" -Type String
  Set-ItemProperty -Path "HKCU:\Software\Microsoft\Windows\CurrentVersion\Media Center\Settings\ProxySettings" -Name "ProxyPort" -Value 8080 -Type DWord

Prevention tip

Always set the proxy mode dropdown to Custom before touching the proxy name field in the UI. That order avoids the error entirely. If you're deploying proxies via Group Policy, push the ProxyMode=2 value along with the name and port — don't leave mode at default 0. The error only bites when you change name without changing mode first. Also, if you're using a local proxy like Fiddler or Charles, note that Media Center doesn't respect Internet Explorer's proxy settings when mode is 0 or 1 — you must use custom mode 2 for any dedicated proxy.