Sys.Webforms.PageRequestManagerServerErrorException

I have been for the last 3 days engaged in an almost futile attempt to debug a certain AJAX error was apparently emanating from some Telerik ajax controls. this error is manifested quite randomly

Sys.Webforms.PageRequestManagerServerErrorException: An unknown error occurred while processing the request on the server the status code returned on from the server was: 500

Despite countless hours in asp.net and Telerik Rad Control forums , extensive searches using Google and deep diving in reputed ASP.NET blogs, I could not find a resolution to it. Until one of my colleagues decided to do some excavation work on the event viewer and there it was (among many more):

Exception information:

Exception type: ArgumentOutOfRangeException

Exception message: Index was out of range. Must be non-negative and less than the size of the collection.

Parameter name: index

at System.Collections.ArrayList.get_Item(Int32 index)

at Telerik.Web.UI.GridItemCollection.get_Item(Int32 index)

at ECP.CERS.ControlLibrary.PassGrid.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) in G:\SVN All\cers\ECP.CERS\ECP.CERS.ControlLibrary\PassGrid.cs:line 2794

at ECP.CERS.Website.AppCode.PageController.CERSBasePage.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) in G:\SVN All\cers\ECP.CERS\ECP.CERS.Website\AppCode\PageController\CERSBasePage.cs:line 578

at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

To which I breathe a huge sigh of relief and Since then I have rediscovered the use of the eventviewer in debugging code running in production environments. Apparently the message occurs when an asp.net thread dies and it returns the status code 500.

but something is puzzling - Most people seem to have stopped reporting this bug online (it seems to have been quite prevalent circa. 2008-2009) but disappeared - except in my case. strange!!

(FYI: I am using the VS2010 Enterprise, .NET 4.0 Windows 7, latest release of telerik but it was still occurring....strange)

Lesson: Eventviewer is your friend! then Google comes later, the only time Google beats the Eventviewr is when you do search and Google lands you here - coz thats something the eventviewer cannot do :).