I accidentally set a cargo stop on a route that couldn’t be reached. I didn’t notice until a ‘Error’ message came on a depot for Setting all the cars to the route (“Error: Unable to find station”).
I immediately found the section of road missing and replaced it.
I tried again, but got the same Error Message. I next deleted the route and made a new one using the same stops, then tried to set the Horse Wagons to it, again, error, can’t find any stops.
I reset the game and reloaded the save, same situation. Started a new game, same again, the Horse Wagon just won’t budge (Horse Carriages and Trains work, however). Here is an image, you can clearly see the 3 truck stops (one at each industry and one in the town of Filey), and the truck depot in the centre at the t junction.