Validation of viewstate MAC failed


Users get errors on various pages with a referral URL of /Site/Errors/500.aspx. The server Event Viewer contains the content of the detailed error message below.

Steps To Reproduce:

This is due to configuration requirements for a Web Farm. It may occur only after updates (i.e. service pack update) to the ASP.Net framework.


This resolution is addressed in the following article for setting up load balancing with Project Insight:

Affected Versions:



Detailed Error Message

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.

Online 1/4/2010
Updated on: