为什么在编译ASP.NET MVC3应用程序时会引发此异常...
类型'System.Web.Mvc.ModelClientValidationRule'存在于'c：\ Program Files \ Microsoft ASP.NET \ ASP.NET网页\ v2.0 \ Assemblies \ System.Web.WebPages.dll'和'c：\ Program Files \ Microsoft ASP.NET \ ASP.NET MVC 3 \ Assemblies \ System.Web.Mvc.dll'