Web Services

I've been meaning to learn some more .NET so tonight I programmed a web service. Nothing very exciting, it calculates the price per square inch for pizza given the preice and diameter.
Unfortunately despite running fine locally when I uploaded it I get 'Server Error in '/' Application' so I can't actually use it. Still I have managed to learn the process. Now I just need to find out why my rented server won't run it but IIS on my laptop does.