After you click "manage attachments" you will see sections where you click "browse" go down and where you see "Upload File from a URL" you copy and paste the attachment link from photobucket there... then click "upload"
Hmm having the same issue,can't upload a pic.But using an iMac with Safari browser,which just slams shut and I'm not logging in.Wonder if I just put the pics on icloud and shared from there if it would work?