Great! So you are getting the results from a table in the database. Are you exporting the results from within Visual Studio or have you deployed the report to your report server? Based on the information that I have so far, it appears to me that you are trying to export from within your local development environment, but I could be off base on this one. I would try to export it from report manager or even by using URL Access.
I personally would try to refresh the dataset (if running locally), test the "query" results and then preview the report in Visual Studio. Be sure that the report actually refreshes by pushing the "refresh" button.
Hopefully this will help you.
Brian K. McDonald, MCDBA, MCSD
Business Intelligence Consultant