Combobox displaying list instance instead of the actual value names

I am populating a combobox with data from database. The data is being stored in a list. When I run the form, the combobox displays the right amount of GroupPlayers i.e. 2 but doesn't actually display the name of these groups, instead it displays the list (i think it's called, correct me if i am wrong) instance i.e. group.

Main form:

    public void Groups() {
        var smallGroups = new List<GroupsPlayers>();

        //sql connections query etc etc is here 

        while(rd.Read())
        {
            var currentPlayer = new GroupsPlayers() {
                GroupID = rd["GroupID"].ToString(),
                GroupName = rd["GroupName"].ToString(),

            };

            smallGroups.Add(currentPlayer);
        }

        if(userResponse == DialogResult.Yes)
        {
            UpdatePlayer frmPlayers = new UpdatePlayer(smallGroups);
        }
    } 

UpdatePlayer form

 public class GroupsPlayers
    {
        public string GroupID { get; set; }
        public string GroupName { get; set; }
    }


List<GroupsPlayers> _GroupPlayers;
UpdatePlayer (List<GroupsPlayers> GroupPlayers)
{
    _GroupPlayers = GroupPlayers; 
}

private void BindCb()
        {
            cb.DataSource = _GroupPlayers;
            cb.DisplayMember = "GroupName";

        }

Also, when I use cb.ValueMemeber = "GroupID"; I get the error

Cannot bind to the new display member