How to Validate Forms with ASP.NET MVC 2 Data Annotations: Listing 6.
Registering the Custom Attribute in Global.asax
Sub Application_Start()
AreaRegistration.RegisterAllAreas()
RegisterRoutes(RouteTable.Routes)
DataAnnotationsModelValidatorProvider.RegisterAdapter(
GetType(WithinDaysAttribute), GetType(WithinDaysValidator))
End Sub