Juri Strumpflohner
Juri Strumpflohner 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.

Server Error: Validation of viewstate MAC failed.

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>
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