Denise,
It seems as if it has something to do with the amount of data that gets posted to the server at a time.
I can upload one feature with one attachment and it works.
But as soon as I edit more than one feature with attachments, and post my updates, the attachments gets left behind,
as well as every attachment I try to post thereafter..
I am really disappointed by the response time from Esri Inc, to help me resolve this issue...