The attachement is set to only the upload path, it does not include the server file name:
set WA_MailObject = WAUE_AddAttachment(WA_MailObject,"" & cStr(Server.MapPath("../public/upload")) & "")
On the attachments tab, click the lightning bolt next to value and select the Server File name variable from the WA Upload Files (File Field) group. Then place you cursor in front of the code that is added and paste the following:
../public/upload/