Hi, If I leave a page open for few hours and then either (1) hit refresh or (2) click on any link on that page, I get the 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.' I get this error many times when I leave a page open and then navigate to a different page. Is there a way to prevent this mac validation error (via web.config file)? I have set 'enableviewstatemac=false' at page level, but it still doesnt help. Any suggestions? In addition, how do I ask the site to redirect to a error friendly page, instead of showing this entire error message to customers? Thanks, Maddy