I have the same problem
I tried the following, after having tried EVERY conceivable path, including even using an actual file name instead of the variable, and nothing worked.
$WA_MailObject = WAUE_AddAttachment($WA_MailObject,"".(realpath("/client_art/".$row_orders['client_art'])) ."");
I finally found this post and tried the above but it doesnt work either.
This is for an image file, and I used the image in the body of the email, which works. I tried that path for the attachment, but it wouldnt work.
When I tried to add the "die" command, nothing at all appeared on the page. Just blank.