KBA-01698: Server Error – Validation of viewstate MAC failed


We are getting a Server Error. What does 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 mean?  We are not using a MAC.


The most common cause of this error is a client-side computer left on overnight on a night when the server was rebooted. It can also happen if the server is updated while the client is open.

In this context MAC does not refer to the Apple ecosystem, but rather to “Message Authentication Code”.

The client computer has a page sent from the server long enough ago that the “MAC” used to generate the page has expired, so when the client sends a request using that page back to the server, the MAC is invalid.


  • Get out of Spitfire and then load it/open it again. This should clear the error message.


KBA-01698; Last updated: September 20, 2021 at 16:32 pm