Entity Framework ObjectDisposedException

Good Day! I use EF 5 Beta 2 CodeFirst. For my entities first I created ConsoleApplication and Repository working well, but when I create dll and use this Repository I have ObjectDisposedException, when tried to use Repository.
Sample (in var user = (new Repository().GetElementById<ReposirotyEF.User>(resultTesting.Users.Id) as ReposirotyEF.User);):

public static ResultModel PopulateResultModel(ResultTesting resultTesting)
{
        string name = string.Empty;

        var user = (new Repository().GetElementById<ReposirotyEF.User>(resultTesting.Users.Id) as ReposirotyEF.User);
        name = user.Name;

        return new ResultModel()
                   {
                       Id = resultTesting.Id,
                       Name = name,
                       Result = resultTesting.Result,
                       Answers = resultTesting.Answers,
                       Data = resultTesting.TimeEnd,
                       RightAnswers = resultTesting.RightAnswers,
                       Time = resultTesting.Time
                   };
    }

Or:

public void SaveOrUpdate<T>(T obj)
    {
        using (var context = new ContextTest1())
        {
            switch (typeof(T).Name)
            {
                case "User":
                    User user = context.Users.ToList().Find(u => u.Id == (obj as User).Id);
                    User newUser = obj as User;
                    if (user != null)
                    {
                        user = newUser;
                    }
                    else
                    {
                        context.Users.Add(newUser);
                    }

                    break;
                case "ResultTesting":
                    var resultTesting = context.ResultTestings.ToList().Find(u => u.Id == (obj as ResultTesting).Id);
                    var newRes = obj as ResultTesting;
                    if (resultTesting != null)
                    {
                        resultTesting = newRes;
                    }
                    else
                    {
                        context.ResultTestings.Add(newRes);
                    }

                    break;
                case "Question":
                    var question = context.Questions.ToList().Find(u => u.Id == (obj as Question).Id);
                    var newQue = obj as Question;
                    if (question != null)
                    {
                        question = newQue;
                    }
                    else
                    {
                        context.Questions.Add(newQue);
                    }

                    break;
                default:
                    //context.CurrentTestings.ToList().Remove(obj as CurrentTesting);
                    var currentTesting = context.CurrentTestings.ToList().Find(u => u.Id == (obj as CurrentTesting).Id);
                    var newCur = obj as CurrentTesting;
                    if (currentTesting != null)
                    {
                        currentTesting = newCur;
                    }
                    else
                    {
                        context.CurrentTestings.Add(newCur);
                    }

                    break;
            }
            context.SaveChanges();
        }
    }

in context.CurrentTestings.Add(newCur);

And my GetElementById (not good):

public IId GetElementById<T>(int id)
        where T : IId
    {
        using (var context = new ContextTest1())
        {
            switch (typeof(T).Name)
            {
                case "User":
                    return context.Users.ToList().Find(u => u.Id == id);
                case "ResultTesting":
                    return context.ResultTestings.ToList().Find(u => u.Id == id);
                case "Question":
                    return context.Questions.ToList().Find(u => u.Id == id);
            }

            return context.CurrentTestings.ToList().Find(u => u.Id == id);
        }
    }

Thx for you help.