List Box Drag and Drop Error

Hello,
I thought I had this done but I keep getting a error on my mouse down event.  Here is the Code I have.

This is how I am populated my First list box
 Private Sub cboFiles_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cboFiles.SelectedIndexChanged
        Try
            Dim mySelDir As New DirectoryInfo(cboFiles.SelectedItem)
            Dim myFilename As FileInfo
            Dim myImageDir(1) As DirectoryInfo
            Dim myText As String

            myImageDir = mySelDir.GetDirectories("Images")

            lstDgnFiles.Items.Clear()
            lblOutPutDir.Text = myImageDir(0).FullName.ToString

            For Each myFilename In mySelDir.GetFiles("*.dgn")
                lstDgnFiles.Items.Add(myFilename)  'Add tostring to get out of the filename
            Next myFilename
        Catch ex As Exception
            MessageBox.Show("The process failed: {0}", ex.ToString())

        End Try

This is my code when I double click a file.  This works fine
  Private Sub lstDgnFiles_DoubleClick(ByVal sender As Object, ByVal e As System.EventArgs) Handles lstDgnFiles.DoubleClick

        lstMakePDF.Items.Add(lstDgnFiles.SelectedItem)

    End Sub


this Code i got from iboutchkine



 Private Sub lstDgnFiles_MouseDown(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles lstDgnFiles.MouseDown

        lstDgnFiles.DoDragDrop(lstDgnFiles.Items(lstDgnFiles.SelectedIndex.ToString()), DragDropEffects.Copy)

    End Sub

    Private Sub lstMakePDF_DragEnter(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles lstMakePDF.DragEnter
        If e.Data().GetDataPresent(DataFormats.Text) Then
            e.Effect() = DragDropEffects.Move
        Else
            e.Effect() = DragDropEffects.None
        End If
    End Sub

    Private Sub lstMakePDF_DragDrop(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles lstMakePDF.DragDrop
        lstMakePDF.SelectedItem = e.Data().GetData(DataFormats.Text).ToString()
    End Sub
End Class