I'm currently investigating a report under similiar circumstances. It works perfect in Visual Studio 2008 but after it's been deployed to SSRS the new parameter I added fails to return any data when populated and even returns 'Arithmetic Overflow' errors when certain values are used.

The best advice I've received so far is to run SQL Profiler on the source database and examine the differences in the query executed between SSRS and VS2008.

Hope this helps, if I find anything further then I'll certainly try to remember to post here! 🙂