ObjectContext实例已被释放，不能再用于需要连接的操作。

我有这个视图：

@model MatchGaming.Models.ProfileQuery
@{
    ViewBag.Title = "Index";
}
Index
    


@using (Html.BeginForm("Results", "Profiles")) {
    @Html.ValidationSummary(true)
    

        
ProfileQuery
        @Html.EditorFor(model=>model.SearchString)
            
    
}
    @Html.ActionLink("Back to List", "Index")

我有这个HttpPost的控制器：

[HttpPost]
public ActionResult Results(ProfileQuery profileQuery)
{
    Debug.Write(profileQuery.SearchString);
    using(var db = new MatchGamingEntities())
    {
        var SearchUserName = db.Users.SingleOrDefault(a=> a.UserName.Contains(profileQuery.SearchString));
        var Users = from m in db.Users
                    join m2 in db.MyProfiles on m.UserId equals m2.UserId
                    where m.UserName == SearchUserName.UserName
                    select new UserViewModel
                    {
                        UserName = m.UserName,
                        LastActivityDate = m.LastActivityDate,
                        Address = m2.Address,
                        City = m2.City,
                        State = m2.State,
                        Zip = m2.Zip
                    };
        return View(Users.AsEnumerable());
    }
}

这是Results的视图：

@model IEnumerable    
@{
    ViewBag.Title = "Results";
}
Results

    
UserViewModel
    @foreach (var item in Model){
    UserName
    @item.UserName
    LastActivityDate
    @String.Format("{0:g}", item.LastActivityDate)
    Address
    @item.Address
    City
    @item.City
    State
    @item.State
    Zip
    @item.Zip
    }

我一直收到这个错误：

The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.

我弄不明白为什么。