Creating Entity Model with Cross Referencing Table

Question

Here are my models:

public partial class NEWS
{
    public NEWS()
    {
    }
    [Key]
    public int NEWSID { get; set; }
    public string Title { get; set; }
    public string Text { get; set; }
    public string InsertDate { get; set; }
    public int GroupingID { get; set; }
    public virtual Subjects Subjects { get; set; }

}

public partial class Subjects
{
    public Subjects()
    { this.NEWSs = new HashSet<NEWS>(); }
    [Key]
    public int GroupingID { get; set; }
    public string Farsi { get; set; }
    public string Latin { get; set; }

    public virtual ICollection<NEWS> NEWSs { get; set; }
}

public class UserGroup
{

    public UserGroup()
    { this.Userss = new HashSet<Users>(); }
    [Key]
    public int UserID { get; set; }
    public string Title { get; set; }
    public virtual ICollection<Users> Userss { get; set; }
}

public class Users
{
    public Users()
    { }
    public string Name { get; set; }
    public string Family { get; set; }
    public string Email { get; set; }
    public string UserName { get; set; }
    public string PassWord { get; set; }
    [Key]
    public int UserID { get; set; }
    public virtual UserGroup UserGroup { get; set; }

    // public HashSet<Users> Userss { get; set; }
}

public class NEWSDBContext : DbContext
{
    public NEWSDBContext()
        : base()
    {
        Database.SetInitializer<NEWSDBContext>(null);
    }
    public DbSet<NEWS> NEWSs { get; set; }
    public DbSet<Users> Userss { get; set; }
    public DbSet<UserGroup> UserGroups { get; set; }
    public DbSet<Subjects> Subjectss { get; set; }
}

I always get an error in return View(newss.ToList());:

The underlying provider failed on Open