I have a module that I am developing that gives an error only if a user is logged in, idles at a page too long, then does an action that causes a postback, the "critical error" warning will show up. Behind the scenes, this is caused by a Validation of Viewstate MAC failed. I believe this is related to how DNN stores the user in the viewstate to prevent cross-site forgery. At the end of this article http://www.dnnsoftware.com/wiki/loc/print/page/viewstate it shows enableEventValidation="false". I do not want to do that for security reasons.

This page/module can be accessed without logging in. If the user does not login, the page/module works fine, no matter how long it has been idle, so I pretty sure this relates to the ViewStateUserKey. How can this error be properly caught and handled, preferably without losing what was already entered on the form?

So you are saying that nothing can be done (aside from raising the timeout value which adds a security risk, particularly for public workstations)? Isn't there a way to catch an error in Viewstateuserkey and do a redirect? That was going to be my workaround, but I thought there must be a more elegant way.