Sys.WebForms.PageRequestManager is null or not an object when migrating the Web Application to .Net 4.0

We are facing the issue “Sys.WebForms.PageRequestManager is null or not an object when migrating the Web Application to .Net 4.0”

We have a web application which is using Ajax extension script manager. But when we have migrated the application to .Net 4.0 and running the application it’s giving the JavaScript error

“Sys.WebForms.PageRequestManager is null or not an object when migrating the Web Application to .Net 4.0”

Any information to solve this issue would be appreciated

SOLUTION 1:

Do you installed appropriate version of AJAX extension? Once you migrated older web application to .NET 4, you suppose to install AJAX extension 4.0;

Please click here to download AJAX  extension latest version

SOLUTION 2:

Please set the EnableEventValidation=false as shown below, it will give you the exact reason that is causing this error.

 

<%@ Page Language="C#" EnableEventValidation="false" %>

 

Hope this will help you out!!..