Object reference not set to an instance of an object.

Question : - earlier website was using ASP.NET 2.0 till then code was working fine since we changed it to .NET 4.0, it is giving error
Server Error in '/' Application.
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Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

Stack Trace:


[NullReferenceException: Object reference not set to an instance of an object.]
   ImageViewerHandler.ImageViewerHandler.ProcessRequest(HttpContext context) +226
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +596
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +265

We are using IIS 7 . Please help.

Solution: - I checked about image viewer, they support only asp.net 2.0 , I doubt if you can get it working on asp.net 4.
http://www.codeproject.com/KB/web-image/ThumbViewerControl.aspx