aspx not processed on GET only POST

I have a problem with IIS and .NET 2.0. When I post to an aspx page
everything acts as expected, the page is executed and I get the correct
response. But when I send a GET request IIS just returns the code of the aspx
page.
I tried switching to .NET 1.1 and it did not behave this way.

I have been unable to discover why this happens. Any help would be
appreciated.