“Validation of viewstate MAC failed. If this application is hosted by a Web Far…”

Question

i am facing the dreaded:

Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the

Answer 1

One thing I have come across that causes this issue has to do with the recycling intervals of the app-pools on the webserver.

I found this by looking at the event information in Eventviewer/Application logs and the "Task Category" called "Web Event". Then for the time period that this event took place I looked to see if there were any recycled events that took place just before that (Eventviewer/System logs and the "Source" called "WAS".

By default an app-pool will recycle every 1740 minutes (29 hours). If this recycle happened while a user is busy on the site and send post back to the server, the server no longer recognizes the session/viewstate and rejects what is being posted back.

To overcome this from our perspective is to set the recycle event to happen at a specific time of the day when we don't expect activity on the site. In our case 3am in the morning.

Hope that helps someone out there.