Same problem. If you abort an upload, it can't be deleted as it can't find an item. What I did was go to the main item list "My items", and had to delete it from that list. Only problem is, if you have other revisions of that item, they get deleted too. Not too bad though, as they're usually your previous revisions. If you make a newer revision (after the aborted one), you'll have to lose that too in order to delete the aborted one.