While running a report, mostly the report got completed successfully but some times i am receiving the following ERROR in my log file while exporting to CSV.

[Info] DeliverToSure : Rendering Report (CSV)[Error] Microsoft.ReportingServices.ProcessingCore : ProcessingAbortedException : An error has occurred during report processing.[Error] Microsoft.ReportingServices.ProcessingCore : ReportProcessingException : Query execution failed for dataset 'dataset_ilt_roster_by_course_and_user'.[Error] .Net SqlClient Data Provider : SqlException : A severe error occurred on the current command. The results, if any, should be discarded.Operation cancelled by user.Please help me.Regards,Srini