asp.net mvc

سلام در قسمت 17 مجموعه اول اموزش Asp.net mvc بخش enable-migrations این ارور رو بهم میده 

PM> enable-migrations
System.Runtime.Serialization.SerializationException: Type is not resolved for member 'System.Data.Entity.Migrations.Design.ToolingFacade+GetContextTypeRunner,EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.
   at System.AppDomain.DoCallBack(CrossAppDomainDelegate callBackDelegate)
   at System.Data.Entity.Migrations.Design.ToolingFacade.Run(BaseRunner runner)
   at System.Data.Entity.Migrations.Design.ToolingFacade.GetContextType(String contextTypeName)
   at System.Data.Entity.Migrations.EnableMigrationsCommand.FindContextToEnable(String contextTypeName)
   at System.Data.Entity.Migrations.EnableMigrationsCommand.<>c__DisplayClass2.<.ctor>b__0()
   at System.Data.Entity.Migrations.MigrationsDomainCommand.Execute(Action command)
Type is not resolved for member 'System.Data.Entity.Migrations.Design.ToolingFacade+GetContextTypeRunner,EntityFramework, Version=6.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

لطفا کمک کنید . خیلی هنگ کردم