If SwitchList's car movement algorithms cannot figure out how to direct cars to their destinations, SwitchList prints helpful error messages in the Problems Window. This window only appears when problems are found.
You don't need to fix every one of these errors; they simply indicate that some cars will not be moved because destinations cannot be reached, and some industries will not receive traffic. You can still print switchlists, change details on your layout, and use SwitchList when problems appear.
Here are the problems that can appear in SwitchList:
If an industry's town is 'No Value', then no trains can visit that industry and move the freight car. Change the location of the industry to a valid town so that a train visiting the town can pick up the car. Test.
If a cargo does not have both a source and destination industry or yard, then SwitchList will not know where to move the car. Go to the Cargo tab and change the source or destination to the preferred industry."
Freight cars can only have locations that are in towns on the layout - either on the visible layout or in staging. Cars located in the "imaginary" offline towns can't be picked up by trains. Move the offending cars to a staging yard or town on the layout so that it may be carried to its next destination.
Car X is assigned to be loaded with the named cargo, but that cargo's source industry isn't set. Change the cargo's source industry location from 'No Value' to a valid town.
Car X is loaded with the named cargo, but that cargo's destination industry isn't set. Set the cargo's destination industry.
Because car X has no cargo, it needs to be returned to its source railroad. However, SwitchList doesn't know where to send the car. Mark one of the yards, either in staging or on the layout, as accepting the name division so the car gets routed towards it.
The car needs to be delivered from town Y to town Z, but no combination of trains will take a car like Car X between those towns. Check that a sequence of trains exist that would go between the towns, and make sure both will carry cars of the same car type as X.
A combination of trains will take cars from X to Y, but no combination of trains will take cars of type Z. Make sure that some trains exist that will carry such cars.
The car is being routed on to the named train, but the train's maximum length has already been reached and more cars cannot be carried. Check that your maximum train length value is appropriate. Consider limiting the number of cars on the offending train by (1) defining new trains to handle some of the overflowing train's work, (2) increasing the maximum train length, or (3) limiting the number of cargos sending freight cars to the towns along the train's path.
The car is being taken to location Y, but the spur is full (or will be full). The car will be left at its current location. Check that the spur's length is correct, and check whether the number of cargos going to the industry is too high for the spur length.
User Interface: Industries Tab for details on setting the town where an industry sits.
User Interface: Yards Tab for details on setting the town where a yard sits.