warning occurring following move from classic to integrated on IIS7 - iis-7

Question

I have migrated my c# asp.net web application from .net 3.5 to .net 4.0 and also changed the IIS7 application pool it runs to be Integrated rather than classic. The site runs fine but I have found the following warning been recorded in the server event log:
Event code: 3005
Event message: An unhandled exception has occurred.
Event time: 26/09/2011 11:19:10
Event time (UTC): 26/09/2011 10:19:10
Event ID: 5e750da6db8544feaede11ed88c072f6
Event sequence: 2
Event occurrence: 1
Event detail code: 0
Application information:
Application domain: /LM/W3SVC/3/ROOT-2-129615059474458846
Trust level: Full
Application Virtual Path: /
Application Path: << REMOVED >>
Machine name: << REMOVED >>
Process information:
Process ID: 5864
Process name: w3wp.exe
Account name: << REMOVED >>\app_user
Exception information:
Exception type: NullReferenceException
Exception message: Object reference not set to an instance of an object.
at System.Web.HttpApplication.set_AsyncResult(HttpAsyncResult value)
at System.Web.HttpApplication.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData)
at System.Web.HttpRuntime.ProcessRequestInternal(HttpWorkerRequest wr)
Request information:
Request URL: http://127.0.0.1/dummy.context
Request path: /dummy.context
User host address: 127.0.0.1
User:
Is authenticated: False
Authentication Type:
Thread account name: << REMOVED >>\app_user
Thread information:
Thread ID: 22
Thread account name: << REMOVED >>\app_user
Is impersonating: False
Stack trace: at System.Web.HttpApplication.set_AsyncResult(HttpAsyncResult value)
at System.Web.HttpApplication.System.Web.IHttpAsyncHandler.BeginProcessRequest(HttpContext context, AsyncCallback cb, Object extraData)
at System.Web.HttpRuntime.ProcessRequestInternal(HttpWorkerRequest wr)
Custom event details:
Any ideas what may be causing this as I am stumped as to what it might be?

Answer 1

(tech difficulty: I'm having trouble to add a comment to yr question but it seems I can add it as an ansewer)
I am experiencing the same error. In this link https://jira.springsource.org/browse/SPRNET-1456 they say it's a bug that "won't be fixed"

Answer 2

I had this error and looked in the Event Viewer. Among several other errors, I had this one and another (which was an Information) :
Information 14/11/2011 13:54:04 Windows Error Reporting 1001 None
details:
Fault bucket , type 0
Event Name: CLR20r3
Response: Not available
Cab Id: 0
Problem signature:
P1: w3wp.exe
P2: 7.5.7601.17514
P3: 4ce7afa2
P4: mscorlib
P5: 4.0.0.0
P6: 4e1823db
P7: f5
P8: 9
P9: System.StackOverflowException
P10:
Attached files:
These files may be available here:
C:\ProgramData\Microsoft\Windows\WER\ReportQueue\AppCrash_w3wp.exe_426513163e392f7b5e2712abb67e65a456d0f5_015c843b
Analysis symbol:
Rechecking for solution: 0
Report Id: b8a9aec0-0ebf-11e1-86d9-001d927c2d4c
Report Status: 0
So it was a stackoverflow. I guess that the error you see is just an artifact of another error. You should try to investigate for this other error. I don't say it will be a stackoverflow like mine, but it could be something else.