I have a couple of Web Application/Web Projects created with ASP .NET 4.0 that I work on at home. I opened one up at work today, and whenever I try to debug the project, or right-click -> “View in Browser” an individual webpage, I receive the “503 Service Unavailable” error with “Failed to connect to server localhost” as the full error message.
Now, I’ve tried numerous of the common fixes, including:
- Re-registering .NET Framework 4.0
- Re-downloading .NET Framework 4.0
- Made sure localhost wasn’t pointing to another location
- Made sure the .NET Extensibility option was checked under the IIS features (IIS -> World Wide Web Servies -> Application Development Features).
- Allowed the ASP .NET v4.0.xxxx setting under “ISAPI and CGI Restrictions” in the IIS Manager.
Yet nothing seems to have worked, yet. The only difference in scenarios where these pages work, and they don’t, is the computer I’m opening them on. I’m thinking it may be a Firewall setting, but I’m not too sure what. Any help would be greatly appreciated.
Finally discovered the solution to this problem, figured I would share in-case anyone else encounters the same kind of situation. It turns out this was a browser proxy issue.
If you can’t connect to localhost when debugging ASP sites in Visual Studio, change the following settings:
Firefox: Options -> Advanced -> Network -> Settings
Select either “No Proxy” or “Auto-detect proxy settings for this network”. When I was receiving this error, it was set to “Use system proxy settings” (I never manually changed this, an update must have).
Internet Explorer: Internet Options -> Connections -> LAN Settings
If it’s checked, try unchecking “Use Automatic configuration script”. This solved this issue for me, and once again, ASP .NET use to work and I never changed this setting.