IIS configuration issue

For some reason, with Windows 2003 Standard Server, if a site upgrades to
dotnet 2.0, certain file types, .exe, .zip, .dll, will no longer prompt to be
saved or opene, but return a Server Error, usually 404 or 400

Any ideas??

We have checked for IIS_WPG permissions and mime types, and other obvious
fixes in the past, but are stumped this time.
--
Emil Caruthers