Please follow this , hope this will give you detailed error..., or Have you checked is error is related to TimeOut to run your query ?,Need some more detail on error
Enable remote errors through SQL Server Management Studio
Start Management Studio and connect to a report server instance. For more information, see How to: Connect to a Report Server in Management Studio in SQL Server Books Online.
Right-click the report server node, and select Properties.
Click Advanced to open the properties page. For more information, see Server Properties (Advanced Page) - Reporting Servicesin SQL Server Books Online.
In EnableRemoteErrors, select True.