Problem:

You think you have completed all your destinations, but the games didn't count one as valid.

Explanation:

In the US and Europe map, there are some places that can be misleading, like Nashville – Atlanta. This is due to the way the cities names where laid out on the map, in order to be readable on a computer screen. It is easy to think that you reach Atlanta, but in fact your trains go only to Nashville. Look carefully at the map.