That debug code showed that it was not finding the file. I changed it to the relative path using the following code:
$WA_MailObject = WAUE_AddAttachment($WA_MailObject,"".(realpath("../client_art/".$row_orders['client_art'])) ."");
So... I used ../client_art instead of /client_art and it worked! I'm pretty sure I tried that variation yesterday... but probably not with the exact code you gave me - using the realpath syntax. Thank you very much, and hopefully this will help someone else.
Just a suggestion... the realpath code is not mentioned in the help file for attachments in Universal e-mail documentation, and it looks like it should be. Again, thanks.