“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”
I saw a lot of solutions online, but what worked for me is to have my own statically generated Machine Key on Web.Config file.
Go to http://www.aspnetresources.com/tools/keycreator.aspx (or you can write your own code to do this – try this: http://support.microsoft.com/kb/313091/EN-US/)
Then add the following within System.Web, using the keys returned
<machineKey validationKey=”xsajsjsnajsnajsnasnasnajsajn”
decryptionKey=”sajsnajsnajsnajsnaj” validation=”SHA1″ />
