404 Errors When Upgrading ASP.NET 3.5 Web Sites to ASP.NET 4.0

by jmorris 20. October 2010 16:19

After upgrading our projects from Visual Studio 2008 to Visual Studio 2010 and modifying our deployment scripts to to use the 4.0 compiler, we ran into another issue with HTTP 404 errors after deploying to our development environment:


Running through the checklist:

  • Is ASP.NET 4.0 Installed? Check!
  • Is ASP.NET 4.0 running? Check!
  • Is IIS running? Check!
  • Is the source code deployed? Check!
  • Is the Web site configured properly in inetmgr? Check!
  • Any host file entries causing problems? No. Check!

Blah, what could be causing this? A comrade of mine (thanks Scott) figured this one out: you have to enable IIS to run the ASP.NET 4.0 extension:


To do enable the ASP.NET 4.0 Extensions, do the following:

  1. Fire up intemgr: Start=>Run=>”Inetmgr”
  2. Select the “Web Services Extension” folder
  3. Locate the ASP.NET v4.0.X entry
  4. Right click on it and select “Allow”

That’s it!

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Jeff Morris

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