c# DataGridview Combobox Comlumn not displaying selected value

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I am using a normal Datagridview but I have a problem with it.
This way I am filling data in my grid and adding combobox column to it

db.DataEntities ss = new db.DataEntities();
  DataGridview1.DataSource = ss.table1.ToList();

  if (!DataGridview1.Columns.Contains("dgcolUser"))
  {
      DataGridViewComboBoxColumn dgcombocolUser = new DataGridViewComboBoxColumn();
      dgcombocolUser.Name = "dgcolUser";

      var listOfAllUsers = ss.secAccountInformations.ToList();
      dgcombocolUser.DataSource = listOfAllUsers;
      dgcombocolUser.DisplayMember = "AccountName";
      dgcombocolUser.ValueMember = "UserId";
      DataGridview1.Columns.Add(dgcombocolUser);
  }

  foreach ( DataGridViewRow dgr in DataGridview1.Rows)
  {
      dgr.Cells["dgcolUser"].Value = dgr.Cells["PermittedUserId"].Value;
  }

I am opening this Form in a MDI parent

Form1 frm = new Form1() { MdiParent = MdiForm1};
frm.Show();

when I open my form it not displaying any selected value in Comboboxcolumn
But when I open my Form frm1 not it MdiParent it display selected value in Comboboxcolumn

Form1 frm = new Form1();
frm.Show();

so is this really happen because it shows data when i am showing my form without MdiParnet or is there any other reason due to which it is not happening<br>
Please give me better suggesstion.. because showing form without MdiParent is not valid solution.