I want to create a module using ajax control toolkit. I am using the Dotnetnuke 5.5.0, VS2010 beta 1,.net framework 4.0 and Ajaxcontroltoolkit.dll 3.0.20820.0 version.When I tried to install ajaxtoolkit 4.0, i could not add it in the vs2010. so i installed ajax3.5 for .net framework3.5. I created a module using ajax 3.5, when i installed this module, i am getting the error as " A critical error has occurred. Object reference not set to an instance of an object.". Then I searched in google and found a blog regarding this error, in that they said use ajaxcontroltoolkit 3.0.20820.0 version.I tried this version also. this also i am getting the same error. how to solve thos error? also can anyone please give a step by step process to use ajax control toolkit in dnn module with simple example(just using TextBoxWatermarkExtender1) . thanks in advance