This indicates the truck model Freightliner Argosy is an old mod. 'motor_brake' parameter was changed to 'engine_brake' a couple of versions ago. You should manually save your game from the home screen and re-load it after a game re-start. This indicates the trailer mod, that you had enabled at some point, is no longer available. This might be the reason for trailer problems.
The 'heavy' attribute was changed to 'valuable' a couple of game versions ago.