An item with the same key has already been added.
   at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
   at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
   at System.Data.Entity.Core.Objects.ObjectStateManager.AddStateManagerTypeMetadata(EntitySet entitySet, ObjectTypeMapping mapping)
   at System.Data.Entity.Core.Objects.ObjectStateManager.GetOrAddStateManagerTypeMetadata(Type entityType, EntitySet entitySet)
   at System.Data.Entity.Core.Objects.ObjectStateManager.AddEntry(IEntityWrapper wrappedObject, EntityKey passedKey, EntitySet entitySet, String argumentName, Boolean isAdded)
   at System.Data.Entity.Core.Common.Internal.Materialization.Shaper.HandleEntityAppendOnly[TEntity](Func`2 constructEntityDelegate, EntityKey entityKey, EntitySet entitySet)
   at lambda_method(Closure , Shaper )
   at System.Data.Entity.Core.Common.Internal.Materialization.Coordinator`1.ReadNextElement(Shaper shaper)
   at System.Data.Entity.Core.Common.Internal.Materialization.Shaper`1.SimpleEnumerator.MoveNext()
   at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
   at DownmagazNet.Controllers.HomeController.HaveLink(String link)
   at DownmagazNet.Controllers.HomeController.ConvertSite_downmagaz_net(String content)
   at DownmagazNet.Controllers.HomeController.Proxy(String link)