ASP.NET MVC does not help you to display validation errors, or perform browser redirects, if the browser postback used Ajax instead of a normal form post. The following code deals with these situations. Use ajax_ProcessSuccess as the OnSuccess callback for Ajax.BeginForm (see http://bradwilson.typepad.com/blog/2010/10/mvc3-unobtrusive-ajax.html). Apply the AjaxResult attribute to MVC actions if you want their results to be translated into JSON when invoked over Ajax.