Your error is a friendly error message, it doesnt explain the exact error in detail. Go into tools/internet options/advanced and uncheck the box that says 'show friendly http errors' Now you will get more detailed error messages. Post this message and we can tell you exactly what IIS setting you havnt addressed - I believe your problem is an IIS issue. There is a big difference between IIS on WIN 20003 (IIS 6.0) and previous versions. Enabling ASP, parent paths, sessions etc...
Wind is your friend