SSRS - Severe error message when running stored procedure

I have a report that runs a stored procedure that takes about an hour to run.

After about 30 minutes I get this error message on the report body:

An error has occurred during report processing.
Query execution failed for data set 'DEV'.
A severe error occurred on the current command. The results, if any, should be discarded. Operation cancelled by user. 

The sam开发者_开发问答e stored procedure runs fine when I run it from SQL Server management studio (with the same login credentials the report runs under).

Any ideas what could be causing this? I tried increasing the timeout value on the report but that didn't help.

This just sounds like a timeout. May I suggest you don't base a SSRS report on a stored proc that takes so long to run. You could schedule a daily job to populate a table (or tables) containing this report data and point the report at this table. That way it doesn't have to recalculate the data every time.

You can find the logs in your SQL Server installation directory. example: C:\Program Files\Microsoft SQL Server\MSRS10.REPORTING\Reporting Services\LogFiles

This might help.

http://blogs.msdn.com/b/jgalla/archive/2006/10/11/session-timeout-during-execution.aspx

Check your connection string for the report. I got this error when I had used a malformed connection string. i.e. I had "Server=" when I should have had "Data Source=".