Box.com is still not working properly in version 5.20140227 (I'm using it in Debian testing and sid).
I created a new clean repository and configured Box.com (everything from the webapp). At first it seamed to work, files where being uploaded and the logs where fine. Then I created another clean repository in another computer and started syncing. Downloading files worked properly, but when trying to upload a file from the second computer I got this: