Untagged files are not processed properly by the uploader. You'll get a "General Upload Error". This also seems to happen when there are multibyte characters in the ID3 tags.
I've had that error occur several times, and then the file finally made it through.
It was from a Russian band, tagged with presumably non-ascii characters, but it finally went through, and I really really doubt they have some of the other things I've uploaded.
