Dropbox files protected by copyright can't be synced and results
in an error. This issue reflects that in the Dropbox's limitations
section to warn rclone users and give info about why this error
occurs due that by default Dropbox API doesn't give enough info.
Proposed by the original repo owner in this comment:
https://github.com/rclone/rclone/issues/2301#issuecomment-388291079
Co-authored-by: Nick Craig-Wood <nick@craig-wood.com>