We encountered an error like:

ReportServerException: The report execution x5pl2245iwvvq055khsxzlj5 has expired or cannot be found. (rsExecutionNotFound)]
   Microsoft.Reporting.WebForms.ServerReportSoapProxy.OnSoapException(SoapException e) +72
   Microsoft.Reporting.WebForms.Internal.Soap.ReportingServices2005.Execution.ProxyMethodInvocation.Execute(RSExecutionConnection connection, ProxyMethod`1 initialMethod, ProxyMethod`1 retryMethod) +428
   Microsoft.Reporting.WebForms.Internal.Soap.ReportingServices2005.Execution.RSExecutionConnection.GetExecutionInfo() +133
   Microsoft.Reporting.WebForms.ServerReport.EnsureExecutionSession() +197
   Microsoft.Reporting.WebForms.ServerReport.LoadViewState(Object viewStateObj) +256
   Microsoft.Reporting.WebForms.ServerReport..ctor(SerializationInfo info, StreamingContext context) +355

[TargetInvocationException: Exception has been thrown by the target of an invocation.]
   System.RuntimeMethodHandle._SerializationInvoke(Object target, SignatureStruct& declaringTypeSig, SerializationInfo info, StreamingContext context) +0
   System.Reflection.RuntimeConstructorInfo.SerializationInvoke(Object target, SerializationInfo info, StreamingContext context) +108
   System.Runtime.Serialization.ObjectManager.CompleteISerializableObject(Object obj, SerializationInfo info, StreamingContext context) +273
   System.Runtime.Serialization.ObjectManager.FixupSpecialObject(ObjectHolder holder) +49
   System.Runtime.Serialization.ObjectManager.DoFixups() +223
   System.Runtime.Serialization.Formatters.Binary.ObjectReader.Deserialize(HeaderHandler handler, __BinaryParser serParser, Boolean fCheck, Boolean isCrossAppDomain, IMethodCallMessage methodCallMessage) +188
   System.Runtime.Serialization.Formatters.Binary.BinaryFormatter.Deserialize(Stream serializationStream, HeaderHandler handler, Boolean fCheck, Boolean isCrossAppDomain, IMethodCallMessage methodCallMessage) +203
   System.Web.Util.AltSerialization.ReadValueFromStream(BinaryReader reader) +788
   System.Web.SessionState.SessionStateItemCollection.ReadValueFromStreamWithAssert() +55
   System.Web.SessionState.SessionStateItemCollection.DeserializeItem(String name, Boolean check) +281
   System.Web.SessionState.SessionStateItemCollection.DeserializeItem(Int32 index) +110
   System.Web.SessionState.SessionStateItemCollection.get_Item(Int32 index) +17
   System.Web.SessionState.HttpSessionStateContainer.get_Item(Int32 index) +13
   System.Web.Util.AspCompatApplicationStep.OnPageStartSessionObjects() +71
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +2065

This error occurs long after the report viewer page has closed. It occurs to any asp.net page in the application, rendering the entire application unusable until the user gets a new session.

The cause of the problem is that the ReportViewer uses session state. When a page retrieves session from any out-of-state session, the session variable of type Microsoft.Reporting.WebForms.ReportHierarchy is deserialized from the session storage. The deserialization could cause the object to connect to the report server when the report is no longer available.

The solution is simple but not pretty. We need to clean up the session variable when the report viewer page is closed. One way is to add some Javascript to the page to handle the window.onunload event. In the event handler, call a web service to clean up the session variable. The name of the session variable appears to be randomly generated. So we need to loop through the session variable to find a variable of the type Microsoft.Reporting.WebForms.ReportHierarchy. Microsoft has implemented pinging between the report viewer and the report server to keep the report alive on the server when the report viewer is up; I hope they will go one step further to take care of this problem.