When browsing on your site you get the following error:

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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.
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According to Microsoft Connect,this is caused by an encrypted viewstate bug in ASP.NET 2/3/3.5.

In order to resolve this issue, you will need to edit your web.config file and make the following changes:

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