I am quite new to ASP.NET too, I had the same problem as you 500, I have tried everything, I unchecked the Show user friendly error messages checkbox (something like this) in Options of IExplorer. Although I wasn't able to find any solution - I hadn't many problems with complete reinstallation, so I did it, installed it (in this order: 1. IIS, 2. MS VS .NET, 3. MSDE) and fortunately it worked (and works) well. I don't know the behavior of my problem, maybe it could be Frontpage XP installed - now I have no FP and it is okay?