ASP.NET MVC Validation of ViewState MAC failed

Question

After publishing a new build of my ASP.NET MVC web application, I often see this exception thrown when browsing to the site:

System.Web.Mvc.HttpAntiForgeryException:

Answer 1

I too had this problem, and expecting the users to clear their cache, cookies or refreshing the page isn't acceptable.

Adding a machinekey to web.config is will fix this. I used this tool to quickly generate a key so I don't see these errors in development and then I generate one properly when the site goes into production.

http://aspnetresources.com/tools/machineKey