We recently upgraded SQL Server Reporting Services for a large SSRS user from SQL 2008 to SQL 2008R2 Gold  (no SQL 2008R2 patches).

Immediately some reports began to fail with a System.OverflowException.  Sometimes the report would run correctly. Other times the report would fail.  The implementation was 4 load balanced servers on the front end.  Failures were happening on all of the servers, so the problem wasn’t specific to a particular server.

The error that customers would see in SSRS is in the screen shot below:

Looking at the SSRS Error Logs, we found errors like these:

processing!WindowsService_0!165c!05/24/2011-06:00:18:: e ERROR: An exception has occurred in data set 'OutageDataSet'. Details: System.OverflowException: Value was either too large or too small for an Int32.

processing!WindowsService_0!165c!05/24/2011-06:00:18:: e ERROR: Throwing Microsoft.ReportingServices.ReportProcessing.ProcessingAbortedException: , Microsoft.ReportingServices.ReportProcessing.ProcessingAbortedException: An error has occurred during report processing. ---> System.OverflowException: Value was either too large or too small for an Int32.

It was always System.OverflowException: Value was either too large or too small for an int32.

As it turns out, this is a known bug, documented in the KB article (http://support.microsoft.com/kb/2359606).

 There is a work around in the article which tells us to convert a grouping field from int to Cdbl or CLong. However, if you do this – you’ll have to figure out which item needs to be changed. The error message will give you the dataset, but not the column, nor the item within the report that exhibits the problem.

This is fixed in Cumulative Update 4(http://support.microsoft.com/kb/2345451) , which you can download and install immediately. This fix is also included in SQL 2008 R2 SP1, which at the time of this writing, is still in beta.