Validation of viewstate MAC failed

Yet another very teasing issue ASP .Net developers face. Solution is pretty much simple.

Add following link in your web.config file.

<pages enableEventValidation="false" viewStateEncryptionMode="Never">

Above line should be included within section.

OR

if you don't want this solution to implemented on project level then you can add these attribute to the page(Top most line of HTML view) directive of the page which is creating issue.

That means you have to add enableEventValidation="false" viewStateEncryptionMode="Never" in page directive.

For a more detail discussion and more solution about the issue please follow the following link

http://blogs.msdn.com/b/tom/archive/2008/03/14/validation-of-viewstate-mac-failed-error.aspx