Same problem here with 2.2.4. I haven't figured out what's up yet since it's not totally consistant but even though I should have available upload slots I see "upload limit reached" errors all the time. If I go into the stats panel to check if perhaps there are uploads not showing in the main window there aren't any. Sometimes it will allow say two users to upload files from me when just a minute earlier it denied the same person because there weren't enough slots. I've had this same issue on multiple computers now so I know it's not just an isolated problem.