Exception: System.NullReferenceException

"An unhandled exception occurred and the process was terminated. Application ID: /LM/W3SVC/1303255675/ROOT  Process ID: 5112 Exception: System.NullReferenceException"

 error - 2010/11/17 00:12:20 - ASP.NET 2.0.50727.0 (1334) - n/a  "An unhandled exception occurred and the process was terminated. Application ID: /LM/W3SVC/1302395675/ROOT  Process ID: 5112 Exception: System.NullReferenceException
 Message: Object reference not set to an instance of an object. StackTrace:
 at System.Web.SessionState.SessionStateModule.PollLockedSessionCallback(Object
 state) at System.Threading._TimerCallback.TimerCallback_Context(Object state) at  System.Threading.ExecutionContext.runTryCode(Object userData) at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode
 code,
 CleanupCode backoutCode, Object userData) at System.Threading.ExecutionContext.RunInternal(ExecutionContext
 executionContext, ContextCallback callback, Object
 state) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext,  ContextCallback callback, Object state) at System.Threading._TimerCallback.PerformTimerCallback(Object
 state)"

Possible Solution:
This might be an InProc Session State issue.  This Microsoft Support Fix might help.  Check it out.
http://support.microsoft.com/kb/942086

Check this link as well.  Here is a discussion on similar problem and may provide some clue: http://forums.asp.net/t/1132396.aspx

Also, its a possibility when a heavy load on the web server and you are using InProc, can cause this problem. You can try editing your Session State using State Server
http://msdn.microsoft.com/en-us/library/ms178586.aspx

****AS IS**** ; Please apply at your own risk.