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If you are upgrading the DNN from 07.03.02 to Version 09.XX.XX and post upgrade you are getting the following error  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:  DotNetNuke.Web.Mvc.MvcHttpModule.SuppressXFrameOptionsHeaderIfPresentInConfig() +327 DotNetNuke.Web.Mvc.MvcHttpModule.Init(HttpApplication context) +13 System.Web.Http ...

With the advent of MVC it is imperative for all programmers to understand the different ways this framework provides to share data from Controller to View. Each solution has its pros and cons. But my advice to you is stick to the method which is most comfortable to you and accepted by your team lead.

Some of the biggest advantages of ASP.NET MVC are that it is built on a solid tried and tested MVC architecture and the removal of view state concept. Added to that is the beautiful concept of separation of concern through Views and Controllers. Microsoft keeps on adding to this frame work and in a very short period of time it has reached its version 5. We look into some new features introduced in version 5 and version 5.1. This information has been gathered from Microsoft site and msdn.