Which line is giving you the error? Does ProblemCategoryList really exist in the DB? Does it require a parameter and you aren't passing it?

One thing I do when I get that cryptic message is start up Profiler and watch to see exactly what the application is passing to SQL Server. That usually gives a good idea of what is happening. If I can't figure it all out from there, I copy the necessary lines from Profiler into Query Analyzer to test it from there. QA seems to give a lot better information about errors.