ObjectSet.AddObject(T) problem?

The ObjectSet.Single(predicate) doesn't work (the Where() and toList() methods as well) unless i write it this way:

ObjectSet.Cast<TEntity>().Single<TEntity>(predicate)

But i don't know what to do to resolve the problem with the AddObject and DeleteObject methods:

public void Add<TEntity>(TEntity entity)
    {
        ObjectSet.AddObjec开发者_StackOverflow社区t(entity);
    }

The error message tells me that "entity" is a wrong argument. Is the problem related to EF 4.1?

---

Here are a few snippets from my generic repository:

public void Add<K>(K entity) where K : class
{            
    context.CreateObjectSet<K>().AddObject(entity);
}

public K SingleOrDefault<K>(Expression<Func<K, bool>> predicate) where K : class
{
    K entity = context.CreateObjectSet<K>().SingleOrDefault<K>(predicate);

    return entity;
}

Please see the link below: http://msdn.microsoft.com/en-us/library/dd382944.aspx

Edit: If you already have a created ObjectSet then your class already defines TEntity, therefor your method should be adjusted as such:

public void Add(TEntity entity)
{
    ObjectSet.AddObject(entity);
}

You should also be able to make similar adjustment to your Single() method, there should be no need for a cast.