Have you tried using breakpoints to step through the code and see exactly what happens, and whether all mappings are correct? There's various points where things could go wrong, and it's quite hard for us to try and help you out if we do not know where to start looking.
You can also try a reverse process, where you use Sql Server Management Studio to fire off your stored procedures with manually added parameters. If that doesn't work, focus on the procedure. If it does, fire up SQL Profiler, and verify that the proper parameters are fed to the procedure by the site. If they aren't, ensure the mapping for the proper fields to the proper parameters is in place, and work backwards that way.
HTH.
Peter
http://entropia-online.blogspot.com/