I have this problem occasionally too and I've been looking into it a lot with Tom. I gave him the results of my findings but nothing's come of it yet. He might look into it more in the AP redesign. It's nothing to do with the file, I've submitted the same 'blank' track with two different accounts and sometimes one works and the other doesn't. Bizarly it's something to do with the ID3 info attached to the file. That is, the track title and author etc. If you're going to resubmit a track, try giving it a different name.
btw this has been discussed a lot of times before, do a search to check a similar thread hasn't already been started before you post. Here's one I started earlier.