If you are looking solution for one of the weird 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.” I can feel your pain. Few days back I was on same position where you are standing now. I was stuck and clearly had no Idea why application getting this error on only some pages where whole application was working fine.