try changing line 25 of the WAUE_emailform_1.php file:
$WA_MailObject = WAUE_AddAttachment($WA_MailObject,"".(realpath("attachment_folder/".$WA_DFP_UploadStatus["WA_UploadResult1"]["serverFileName"])) ." ");
to:
$WA_MailObject = WAUE_AddAttachment($WA_MailObject,"".(realpath("../".$WA_DFP_UploadStatus["WA_UploadResult1"]["serverFileName"])) ." ");