Today I got an exception in a report using SQL Server Reporting Services 2008 R2, but only when attempting to go to the last page of a large report: The report execution sgjahs45wg5vkmi05lq4zaee has expired or cannot be found.;
Digging into the logs I found this:library!ReportServer_0-47!149c!12/06/2012-12:37:58:: e ERROR: Throwing Microsoft.ReportingServices.Diagnostics.Utilities.ReportServerStorageException: , An error occurred within the report server database. This may be due to a connection failure, timeout or low disk condition within the database.;
I knew it wasn't a network problem or timeout because I could repeat the problem at will. I checked the disk space and that seemed fine as well. The real issue was a lack of memory on the database server that had the ReportServer database. Restarting the SQL Server engine freed up plenty of RAM and the problem immediately went away.