Getting a 404 when using .NET 4 on IIS 6, with or without MVC

Question

I\'ve completed this set up on a fair few IIS 6 boxes, but one is giving me a tough time.

The problem occurs when I add the application extension mapping to:

Answer 1

Go into Web Service Extensions in IIS and set ASP.NET 4.0 to Allowed instead of Prohibited.

Like this:

BTW: This happened to me in the RTM version of .net 4 as well, so it's not just the betas.