Nerovision Express 3 shuts down.

Sometimes when i select: make your own DVD-VIDEO which then takes me to Express 3 all functions OK. On other occasions it shuts down and gives me an error code 157, does anyone know what this means? On other occasions all disappears from screen but when i try to reselect i get the message that the programme is already running. I have to log off and on or reboot to get programme back.