Private Sub Grid1_CellValidating(ByVal sender As Object, ByVal e As _
  System.Windows.Forms.DataGridViewCellValidatingEventArgs) Handles _
  Grid1.CellValidating
        If Grid1.Columns(e.ColumnIndex).Name = "Nr" Then
             If IsNumeric(e.FormattedValue) = False Then
                    MsgBox("Sie müssen eine Zahl eingeben!")
                    e.Cancel = True
                End If
            End If
 End Sub