HI, I have a web application that is used by the company I work for. It is running on a Windows 2008 r2 server with IIS 7. I just started getting this error on one web page today, only on two users machines that I know of (mine included), it works on all otheres I have checked. I only get the error when using IE 9, I get no error if I hit the same page from Firefox.
The only clue I have is that server updates were performed this weekend, service packs installed, etc. I tried clearing out my cache. I'm stumped, any ideas?
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.