PHP Warning: move_uploaded_file(): Unable to move
That error does seem specifically related to an ownership/ permissions issue. Your permissions seem fine, so it must be something to do with ownership.
See this link:
https://stackoverflow.com/questions/13723174/php-warning-move-uploaded-file-unable-to-move
Actually, it may be a Ubuntu thing. It may help to set the user and group to www-data. I have found a few search results where this worked for Ubuntu users:
# chown -R www-data:www-data /path/to/uploads