I think the problem is in timerSave_Tick, if, for some reason you haven't already valued Me.PictureBox1.Image in timerCapture_Tick, it would throw NullReferenceException while trying to access to PictureBox1.Image.
Try to modify it in such way:
Private Sub timerSave_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles timerSave.Tick
If(Me.PictureBox1.Image IsNot Nothing) Then
Me.PictureBox1.Image.Save("d:\\capture.bmp")
End If
End Sub
Anyway, you should be able to debug under Visual Studio, to see where the Exception is thrown..