Sequence Contains more than one element.

Hi Vulpes, still remember my post on employee profile? I made some modification, I added a repository on my project.
         public virtual TObject Create(TObject TObject)
        {
            var newEntry = DbSet.Add(TObject);
            return newEntry;
        }

        public virtual int Commit()
        {
            if (!shareContext)
                return _database.SaveChanges();
            return 0;
        }

To insert the record to the database from csv

             try
            {
                foreach(Employee ep in profile)
                {
                   _employeeData.Create(ep);
                }
                _employeeData.Commit();
            }
            catch(Exception ex)
            {
                System.Diagnostics.Debug.Write(ex.StackTrace);
            }

As Nattudurai said, the Single() extension method requires there to be exactly one matching element. If there's more than one, it throws an exception.

So, if you just want to get one element, use First() instead.

Here's the stack trace  
at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source)
   at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.GetQualifiedTableName(XDocument model, String entitySetName)
   at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.b__6d(<>f__AnonymousType2c`2 <>h__TransparentIdentifier62)
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Linq.Enumerable.d__31`3.MoveNext()
   at System.Linq.Enumerable.d__71`1.MoveNext()
   at System.Linq.Enumerable.d__71`1.MoveNext()
   at System.Linq.Enumerable.d__81`1.MoveNext()
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at System.Data.Entity.Migrations.Infrastructure.EdmModelDiffer.Diff(XDocument sourceModel, XDocument targetModel, String connectionString)
   at System.Data.Entity.Internal.InternalContext.ModelMatches(XDocument model)
   at System.Data.Entity.Internal.ModelCompatibilityChecker.CompatibleWithModel(InternalContext internalContext, ModelHashCalculator modelHashCalculator, Boolean throwIfNoMetadata)
   at System.Data.Entity.Internal.InternalContext.CompatibleWithModel(Boolean throwIfNoMetadata)
   at System.Data.Entity.Database.CompatibleWithModel(Boolean throwIfNoMetadata)
   at System.Data.Entity.CreateDatabaseIfNotExists`1.InitializeDatabase(TContext context)
   at System.Data.Entity.Internal.InternalContext.<>c__DisplayClass8.b__6()
   at System.Data.Entity.Internal.InternalContext.PerformInitializationAction(Action action)
   at System.Data.Entity.Internal.InternalContext.PerformDatabaseInitialization()
   at System.Data.Entity.Internal.LazyInternalContext.b__4(InternalContext c)
   at System.Data.Entity.Internal.RetryAction`1.PerformAction(TInput input)
   at System.Data.Entity.Internal.LazyInternalContext.InitializeDatabaseAction(Action`1 action)
   at System.Data.Entity.Internal.LazyInternalContext.InitializeDatabase()
   at System.Data.Entity.Internal.InternalContext.Initialize()
   at System.Data.Entity.Internal.InternalContext.GetEntitySetAndBaseTypeForType(Type entityType)
   at System.Data.Entity.Internal.Linq.InternalSet`1.Initialize()
   at System.Data.Entity.Internal.Linq.InternalSet`1.get_InternalContext()
   at System.Data.Entity.Internal.Linq.InternalSet`1.ActOnSet(Action action, EntityState newState, Object entity, String methodName)
   at System.Data.Entity.Internal.Linq.InternalSet`1.Add(Object entity)
   at System.Data.Entity.DbSet`1.Add(TEntity entity)
   at UpdateRepository`1.Create(TObject TObject) in

HI,

Single and SingleOrDefault are designed to throw if more that one match exists in the sequence. A consequence of this is that the entire sequence must be iterated prior to completion. It does not sound like this is what you want. Try FirstOrDefault instead:

Feature f = o.Features
    .FirstOrDefault(e => e.vcr_LinkName == PageLink && e.bit_Activate == true);

This will (generally) perform better because it completes as soon as a match is found.

Please mark this answer as accepted answer if it resolves your problem.