program shut down when looping datagrid

[Magnus]

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