Some people reported problems with MvcValidatorToolkit when using strongly typed ViewData:
DataBinding: 'MvcValidatorToolkit.SampleSite.Sample3ViewData' doesn't contain property 'Sample3ValidationSet'.
The answer is to put additional property in your viewData:
public class Sample3ViewData
public Sample3ValidationSet Sample3ValidationSet
The view definition looks as follows:
public partial class Sample3 : ViewPage<Sample3ViewData>
Additional example for this scenario can be found on MvcValidatorToolkit site.