Invalid Viewstate errors when hosting on a Web Farm

Everybody has seen the dreaded 'Invalid Viewstate' error from time to time. There are many reasons this can occur. If you host your site on multiple hosts behind a content switch on a web farm you will immediately receive these errors in bulk.

There is an easy solution to this problem:

1. Generate 2 unique HEX keys using this program.

2. Change the \Windows\Microsoft.NET\Framework\<.NET version>\CONFIG\machine.config file on each host in your web farm and add this entry (use your generated keys):

<system.web>

<machineKey validationKey="thekey" decryptionKey="thekey" validation="SHA1"/>

</system.web>