You mean service unavailable?
Recently I had similar error message (because of mixing ASP.NET 1.0 and ASP.NET 2.0 on the server) and the following steps solved the problem:
1. Reinstall asp.net 2.0:
v2.0.50727 - your asp.net 2.0 may be different!
2. Go to Internet Information Services Manager and make sure that ASP.NET 2.0 is enabled (under Web Service Extension). Restart IIS
you may find useful information here: