I’ve pasted the applet source code you posted into my GW6.5/Formativ 1.6 Admin installation, and have been able to run the applet successfully. An ‘unknown error’ is normally something that comes deep from within the GroupWise API which Formativ is sitting over. In your case, it appears there is a problem accessing the MailBox folder in your account. Accessing this folder is a fundamental step taken by many applets, and the failure would tend to indicate some type of fundamental error with your account. There are certainly no known issues accessing the Mailbox folder in this way.
I would suggest you try the same applet while logged into another users account, prefereably on the same PC. If this works you most likely have an account problem that may be fixable by performing account maintenance.
If it doesn’t work, try the same operation on another computer if possible.
Once this problem is sorted, adding attachments is quite simple. Given the draft message object returned from the line:
set objMail = GroupWise.Account.MailBox.Messages.Add(...
you would access the objMail .Attachments property. For example:
(This is untested psudocode – but it should point you in the right direction).
Documentation for the message attachments property can be found here.
Please let me know how you proceed with the MailBox access problem.