When coupling up to the box vans on NTP once coupled I am unable to move the wagons. Have checked and all breaks are released. Tried full throttle still no movement. This is happening with both the gronk and class 47 that I have noticed so far makes completing a service impossible!!
This might be a shot in the dark, but do you have the right braking type selected? In one of the cabs there's a selector and vans (as far as I remember) have vacuum brakes, while the locos are usually set in air brakes. Releasing air brakes basically applies vacuum brakes.
You have to use vacuum brakes for the Vans. As far as I can say it is also mentioned in the service description ahead of the start of the service.