program shut down when looping datagrid

Hi I have a datagrid that have checkboxes added to it and there is also a button that I want to use as a check what rows has been selected in the datagrid. But when I use this piece if code the program just close when I press the button that is supposed to show the selected rows in the datagrid Public Function GetSelectedRows(ByVal dg As DataGrid) As System.Collections.ArrayList Dim al As New ArrayList Dim cm As CurrencyManager = Me.BindingContext(dg.DataSource, dg.DataMember) Dim dv As DataView = CType(cm.List, DataView) Dim i As Integer For i = 0 To dv.Count - 1 If dg.IsSelected(i) Then al.Add(i) End If End Next Return al End Function ''GetSelectedRows Private Sub btnMakePDF_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnMakePDF.Click Dim s As String = "Selected rows:" Dim o As Object For Each o In GetSelectedRows(MyDataGrid) s += " " + o.ToString() Next o MessageBox.Show(s) ''MessageBox.Show("Selected items....") End Sub ''button1_Click Does anyone know why? Regards Magnus