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.

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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.

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

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This might help.

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

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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=".