asp.net failed to run in dot net 4.0

The website was developed in dot net 3.5 SP1 and running ok within dot net 3.5 SP1. But, after recompiled it into dot net 4.0 and changed the app pool to "integrated", it failed to run. The symptom is that the website was running ok for few minutes. Then, the following message will appear:

[NullReferenceException: Object reference not set to an instance of an object.]

System.Web.PipelineStepManager.ResumeSteps(Exception error) +197

System.Web.HttpApplication.开发者_运维问答BeginProcessRequestNotification(HttpContext context, AsyncCallback cb) +89

System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +189

If we recycle the app pool, it will work for a few minutes and then same error appear.

Any help is appreciated.

Lau.

From the call stack I think this exception was caused by a problematic HTTP module or handler.

You should be able to debug using Visual Studio or WinDbg.