Solution for Error 'Validation of viewstate MAC failed'

Another irritating (funny though) error message developers encountered while developing an ASP.NET application.

I've been caught by this error the first time and it haunted me or irritated me for few hours. Not sure what I did wrong it just happened. This usually happened to freshly deployed application to LIVE Environment if I remember it correctly.


ERROR MESSAGE:

Server Error in '/' Application.
--------------------------------------------------------------------------------

Validation of viewstate MAC failed. If this application is hosted by a
Web Farm or cluster, ensure that < machineKey > configuration specifies
the same validationKey and validation algorithm. AutoGenerate cannot
be used in a cluster.


SOLUTION:

In web.config, inside the , add the following line:

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

L.