ASP.NET Session state lost after exception - asp.net

Question

I've usually avoided in-proc session state, until this recent project. I think I have a problem where the state is lost after an unhandled exception occurs.
This in itself is odd, since exceptions in the context of a request don't down the worker process. It could be an exception on a background thread or a callback or something but, this is a simple site and there's nothing fancy going on.
The session ID remains the same and Session_Start is not called on the subsequent request (so the WP hasn't recycled).
I have quite a lot of logging enabled, and its plain to see that I get an exception from the data tier, its an HttpException inside a HttpUnhandleException, then when I browse immediately after to the home page, the request logs a warning about the missing state.
Worse. This doesn't happen on my dev box (IIS Express), only in QA.
Edit:
Here's a chunk of log:
2013-06-12 13:44:29,975 [23] FATAL MvcApplication 100.100.100.100 pxtgn GET An unhandled exception occurred in the web application. The full exception will be unrolled below.
2013-06-12 13:44:30,897 [23] FATAL MvcApplication 100.100.100.100 pxtgn GET Exception.Type: HttpUnhandledException
Exception.Source: System.Web
Exception.Message: Exception of type 'System.Web.HttpUnhandledException' was thrown.
Exception.StackTrace: at System.Web.UI.Page.HandleError(Exception e)
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
at System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
at System.Web.HttpContext.InvokeCancellableCallback(WaitCallback callback, Object state)
at System.Web.UI.Page.LegacyAsyncPageBeginProcessRequest(HttpContext context, AsyncCallback callback, Object extraData)
at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
Exception.Type: HttpException
Exception.Source: CompanyNameProductName.MvcCoreApp
Exception.Message: An error was reported by the data layer: 0Image not found1-10.1007_978-1-4471-4294-2_21-16
Exception.StackTrace: at CompanyName.CompanyNameProductName.imagedetail.Page_Load(Object sender, EventArgs e) in c:\DATA\Git\ProductName\CompanyNameProductNameMvc\imagedetail.aspx.cs:line 55
at System.Web.UI.Control.LoadRecursive()
at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
2013-06-12 13:45:07,913 [25] DEBUG StandardPage 100.100.100.100 pxtgn GET Initializing page 'default_aspx' for GET with query string:
2013-06-12 13:45:07,913 [25] ERROR StandardPage 100.100.100.100 pxtgn GET No User instance in session state. Check the log for signs that the session was started properly since a User object should aways exist in session state, setup via session start events in ASP.NET.
The last line shows the missing state condition. The pxtgn is the first 5 chars from the session ID. I hit a page for which I know the data layer will barf about the non-existent image ID. Then any page I hit next will cause my check to log the problem with the missing state. The check and state reference is in the code for the master page, so I can hit any page to see the problem. This also means the custom error page doesn't work - which is sort of how I came to find the bug.
I've now added a Session.Abandon() after the check and respond with a 500 to get me out of jail, but its quite an odd problem. I'm new to the codebase, and I think I've checked everywhere for the session being cleared or state being overwritten.

Answer 1

1 Thread is destroyed
2 Asynchronous environment
use httpcontext as a Parameter
not system.web.**.httpcontext