Urg. Does your top left cell have a comment in it?

If not, you need to make sure you check before trying to run a command on the non-existent Comment object. Consider the following code snippet:

$comment = $Sheet->Cells($row,$col)->Comment;
if ($comment)
{
    $commenttxt = $comment->Text();
}
[download]

The Text function call fails if there isn't a Comment object stored in your cell. And crashes the script. Duh. I should have thought of this a lot earlier. Or tested.