.com virtual directory gets page cannot be displayed

I am using IIS in XP as a localhost to develop and test websites with ASP.NET.

I have set up successfully many virtual directories with .uk suffixes which
all work. But if I set up a virtual directory with a .com suffix it browsing
to localhost/domain.com gives Page not found with the error: "You have
attempted to execute a CGI, ISAPI, or other executable program from a
directory that does not allow programs to be executed."

The properties of the .com virtual directory are exactly the same as the
properties of the .uk virtual directories and they all access the same files
in the same local path.

Any help much appreciated.

Thanking you in anticipation.

Roger