finally i can debugger to debug the error is from this line of code

  If frmMDI.UltraTabbedMdiManager1.TabGroups.Count > 0 Then
                For i As Integer = 0 To frmMDI.UltraTabbedMdiManager1.TabGroups(0).Tabs.Count - 1
                    If frmMDI.UltraTabbedMdiManager1.TabGroups(0).Tabs(i).Form.GetType.Equals(frmLifter.GetType) Then
                        If frmMDI.UltraTabbedMdiManager1.TabGroups(0).Tabs(i).Form.Text = LifterId Then
                            Dim F As frmLifter = CType(frmMDI.UltraTabbedMdiManager1.TabGroups(0).Tabs(i).Form, frmLifter)

                            If Not F.grdAlarm.DataSource Is Nothing Then

                                Dim DTAlarm As DataTable = CType(F.grdAlarm.DataSource, DataTable)

                                DTAlarm.Rows.Add(New Object() {CDate(DT), StatusId, StatusMsg, BackColor.ToArgb})

                                F.grdAlarm.DataSource = DTAlarm
                                'If DTAlarm.Rows.Count <> 0 Then
                                F.grdAlarm.ActiveRow = F.grdAlarm.Rows(F.grdAlarm.Rows.Count - 1)

                                F.lblAlarm.Text = StatusMsg
                                F.lblAlarm.BackColor = BackColor
                                F.LatestStatusIsBlinking = IsBlinking
                                F.LatestStatusColor = BackColor
                                F.LatestStatusDT = DT
                                frmMDI.tsslStatus.Text = DT & " " & LifterId & ":" & StatusMsg
                                'End If
                            End If

                        End If

                    End If
                Next
            End If

when it come to that line

Dim DTAlarm As DataTable = CType(F.grdAlarm.DataSource, DataTable)

it show me: Datatable internal index is corrupted: 13 

what is the problem?