Attach file from briefcase

Hi, i've uploaded a file in my briefcase trought appCtxt.getUploadDialog() :
this function give me back the followind propriety of the file just uploaded:

.name
.fullname
.notes
.guid
.id
.version
.__internalId
.done

now, i can't attach this file on my new message. On my send function i try to attach the file from the briefcase:


upload_file_id = file.guid;
var node_attach = soapDoc.set("attach", null, node_m);
node_attach.setAttribute("aid",upload_file_id);


but i get:

------
method: [unknown]
msg: upload not found: 33253f3f-5205-41fb-8f74-db207f174d25:07e866b9-4424-44e6-8b3e-778687b153a8
code: mail.NO_SUCH_UPLOAD
detail: soap:Sender
trace: qtp1456226908-8604:https://10.120.120.27:443/service/so...9d3154720f79b8
------

how can i attach a file from the briefcase?

thanks
Marco