Hi, I am using SQL Server 2008 R2 Ent. Edition 64 bit reporting services. The source data for report is at remote server and it is SQL Server 2005 Ent. Edition (though I don't think this matters here.) I have set the <WorkingSetMaximum> to 5GB for SSRS I am testing the performance of report server and running a report with 100K records with 20 concurrent users. All 20 reports gets executed successfully. When I try with 25 or 30 users only 21 reports execute successfully when I see the ExecutionLog table. I see this exception in the report service log file. Please help. ERROR: Throwing Microsoft.ReportingServices.ReportProcessing.ProcessingAbortedException: , Microsoft.ReportingServices.ReportProcessing.ProcessingAbortedException: An error has occurred during report processing. ---> System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index at System.ThrowHelper.ThrowArgumentOutOfRangeException() at System.Collections.Generic.List`1.get_Item(Int32 index) at Microsoft.ReportingServices.ReportIntermediateFormat.Persistence.IntermediateFormatReader.RemoveReadOnlyMembers(List`1 declarations) at Microsoft.ReportingServices.ReportIntermediateFormat.Persistence.IntermediateFormatReader..ctor(Stream str, IRIFObjectCreator rifObjectCreator, GlobalIDOwnerCollection globalIDOwnersFromOtherStream, PersistenceHelper persistenceHelper, List`1 declarations, IntermediateFormatVersion version, PersistenceFlags flags, Boolean initFromStream) at Microsoft.ReportingServices.ReportIntermediateFormat.Persistence.IntermediateFormatReader..ctor(Stream str, IRIFObjectCreator rifObjectCreator, GlobalIDOwnerCollection globalIDOwnersFromOtherStream, PersistenceHelper persistenceHelper, List`1 declarations, IntermediateFormatVersion version, PersistenceFlags flags) at Microsoft.ReportingServices.OnDemandProcessing.Scalability.RIFStorage.SetupStorage() at Microsoft.ReportingServices.OnDemandProcessing.Scalability.RIFStorage.WriteObject(IPersistable obj, Int64 offset, Int64 oldSize) at Microsoft.ReportingServices.OnDemandProcessing.Scalability.StorageItem.Flush(IStorage storage, IIndexStrategy indexStrategy) at Microsoft.ReportingServices.OnDemandProcessing.Scalability.ScalabilityCache.FulfillInProgressFree() at Microsoft.ReportingServices.OnDemandProcessing.Scalability.BaseScalabilityCache.FreeCacheSpace(Int32 count, Int64 freeableBytes) at Microsoft.ReportingServices.OnDemandProcessing.Scalability.BaseScalabilityCache.ReferenceValueCallback(BaseReference reference) at Microsoft.ReportingServices.OnDemandProcessing.Scalability.BaseReference.InternalValue() at Microsoft.ReportingServices.OnDemandProcessing.TablixProcessing.RuntimeDRCollection.FirstPassNextDataRow() at Microsoft.ReportingServices.OnDemandProcessing.TablixProcessing.RuntimeOnDemandDataSet.NextNonAggregateRow() at Microsoft.ReportingServices.OnDemandProcessing.TablixProcessing.RuntimeOnDemandDataSet.ProcessRow(RecordRow row) at Microsoft.ReportingServices.OnDemandProcessing.RuntimeDataSet.ProcessRows() at Microsoft.ReportingServices.OnDemandProcessing.TablixProcessing.RuntimeOnDemandDataSet.Process() at Microsoft.ReportingServices.OnDemandProcessing.RuntimeDataSet.ProcessConcurrent(Object threadSet) --- End of inner exception stack trace ---; SQLearner