Error: Validation of Viewstate MAC Failed

When browsing your site you get the following error:
A critical error has occurred. Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.

This is caused by an encrypted viewstate bug in ASP.NET.

In order to resolve this issue, you will need to edit the following line in your web.config file and set these values to false.  If you are unsure of how to edit your web.config please refer to How to Access Your Web.config.

<pages validateRequest="false" enableViewStateMac="false" enableEventValidation="false">

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