ส่งค่าจาก DataGridview กลับ Main Form MdiParent ไม่ได้

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click

        'New_User.ListBox1.Items.Add(Me.DataGridView1(0, Me.DataGridView1.CurrentCell.RowIndex).Value.ToString())
        Dim selectedRows As List(Of DataGridViewRow) = (From row In DataGridView1.Rows.Cast(Of DataGridViewRow)()
                                                        Where Convert.ToBoolean(row.Cells("checkBoxColumn").Value) = True).ToList()
        For i As Integer = 0 To DataGridView1.Rows.Count - 2
            If DataGridView1.Rows(i).Cells(0).Value IsNot Nothing Then
                New_User.ListBox1.Items.Add(Me.DataGridView1.Rows(i).Cells(0).Value.ToString)
                'New_User.Label7.Text = Me.DataGridView1.Rows(i).Cells(0).Value.ToString
            End If
        Next

        Me.Close()
        'Dispose()

    End Sub

 Private Sub Button1_Click_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim frmNew As New Search_Group
        frmNew.ShowDialog() '= Me.MdiParent
        For i As Integer = 0 To frmNew.DataGridView1.Rows.Count - 2
            If frmNew.DataGridView1.Rows(i).Cells(0).Value IsNot Nothing Then
                ListBox1.Items.Add(frmNew.DataGridView1.Rows(i).Cells("GROUP_USER").Value.ToString())
            End If
        Next

    End Sub