Juri Strumpflohner Follow Juri is a full stack developer and tech lead with a special passion for the web and frontend development. He creates online videos for Egghead.io, writes articles on his blog and for tech magazines, speaks at conferences and holds training workshops. Juri is also a recognized Google Developer Expert in Web Technologies

Server Error: Validation of viewstate MAC failed.

Jul 31, 2009 1 min read

If you get the following error...

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.

You have to specify the "<machinekey>" in your web.config. Actually the error itself already explains it.

<system.web>
    <machineKey validationKey="yourAlphaNumericValidationKey" decryptionKey="yourAlphaNumericDecryptionKey" validation="SHA1"/>
   ...
<system.web>

Questions? Thoughts? Hit me up on Twitter