It appears to happen primarily when the uploads involve large files. That's why some uploads are processed and other fail. As far as I know, the QA and Online teams are working at developing the course of action to test all of the scenarios and cover the possibilities.
You can be assured that when we know more, we'll let this board know.
Sincerely, Paul Burchfield, Genealogy.com Technical Support Find Ultimate Family Tree knowledge base articles, hints, tips, message boards and more at: http://www.uftree.com/UFT/Nav/ufttech.htmlhttp://www.uftree.com/UFT/Nav/ufttech.html