This is just a quickie to see if that helps anybody. The GridView in GeoTwitter had a problem as was using the DataKeyNames. I was getting the error on the viewstate MAC failed error. Looks like adding the code below on the web.config fix the issue.
<pages enableEventValidation="false" viewStateEncryptionMode="Never">
The problem now is I don’t have a validation for the viewstate, that’s a security problem in my modest opinion, I found this resource below that help me to understand a little bit more what the MAC failed error is:
Great blog post found here: Resources to fix the issue.
Hope it helps you too.