Probably a seat or seat belt issue, or possibly fleet monitoring system if fitted. The message is because it thinks there is nobody on the machine, and it is normally due to seat or seat belt(if fitted) switch, but quite often the fleet monitoring systems are wired into the system to prevent use of the machine by making it think nobody is on the machine.
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.