This site is "powered by pagoda", and so was something I built 6 months ago, but pagoda changed the rules, so how are you getting around this new issue?
As several people have reported, COREPATH/classes/log.php makes subdirectories within /fuel/app/logs and this no longer works on pagodabox, even when you add - /fuel/app/logs to their Boxfile.
ErrorException [ Warning ]: mkdir(): Read-only file system
122: mkdir($filepath, \Config::get('file.chmod.folders', 0777), true);
See http://help.pagodabox.com/customer/en/portal/questions/408753-writeable-logs-directory-in-fuelphp?new=408753