Thank you for your reply.
It is a clean install of the extension on a clean install of Dreamweaver on a clean install of Windows 7 :)
The only way it will work is if I add the code for an attachment manually, as in
$WA_MailObject = WAUE_AddAttachment($WA_MailObject,"".$SavePath .".pdf");
only then, can I manage attachments via the UE interface for this particular message without crashing Dreamweaver.
Tried to access the ipvac adress you gave, but the site/page could not load.