If you created your report in SQL Server Business Intelligence Studio, were you able to preview your report there?
If so then you can try to re-deploy your datasource and see if that works. ( you may need to update the project properties so that the 'OverwriteDataSources' property says 'true'.
Also right click on your datasource and make sure you have something like:
Data source=(your sql server name); Initial Catalog=(your database name)
without the brackets in the Connection String part on the General Tab. Also makesure you have added any username and password need to access the server on the Credentials tab.
Rob
