ASP Error: Validation of Viewstate MAC Failed

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ASP Error: "Validation of ViewState MAC Failed" - Causes and Resolutions

Issue
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.

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

Resolution

 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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