Several possibilities here, John. Messages like that generally indicate a vehicle network fault. When you say 'locks down' the car, what do you mean exactly? Are you referring to the car just not starting? The problem is usually the fault is intermittent, and hard to catch in the act with any regularity. That makes it tough. Sometimes the cause is an electrical connection, and sometimes it is one of the modules on the network; in other words, something that upsets the communication on the network.
You will need someone with the proper tools to communicate with the vehicle systems, and a diligent, detective like attitude to get to the bottom of it. YOU will also need to have the patience to let them take the necessary time to catch it, and get the cause isolated.
Good luck!