I'm getting the old "Validation of viewstate MAC failed" error when I click the submit button on my form. (See http://blogs.msdn.com/b/tom/archive/2008/03/14/validation-of-viewstate-mac-failed-error.aspx) The thing is I'm getting the error even when the page is completely loaded (it can be sitting there for five minutes before I hit submit but I still get the error). This isn't even a particularly lengthy page. It uses a DetailsView (which I understand is one of the preconditions for this error), but it's the only databound control on the page. Also, whenever users get this error (which is 100% of the time when they click Submit), they lose their login authentication and have to log back in. This page/site has been in use for about six months but the error suddenly started without any changes being made to the code.
I'm using ASP.net 4 on shared hosting.
Any ideas? Thanks