Page Validation Failed?

After you migrated your web application from v1.1 to v2, one of the problems you might be facing is that the page validation failed.

This is because you do not set the EnableEventValidation property is set to true.
So, in order to have page validation, what you can do is just  set the EnableEventValidation property is set to true. When the property is set to true, ASP.NET allows only the specific events that can be raised on the control during a postback request or callback.

There are couples of way you can set the EnableEventValidation to true.
1. Set the EnableEventValidation property by setting the enabledEventValidation attribute of the @ Page directive or the enableEventValidation attribute of the pages element of the Web.config file.
2. Set the EnableEventValidation property in code, set it in the Page_Init phase of page processing.

It is advisable that you do not disable event validation. If you want to disable the event validation, you have to make sure no postback could be constructed in your application.