What's the problem with Train Simulator?

The original Train Simulator works fine, as does my other add-ons, but I'm having problems with 'The Golden Twenties in Berlin': when I first install the game, I can save activities and go on to the next levels; however, when I re-load the game the next day, it says 'Train simulator cannot be activated! Please close all windows first click ok when ready' :/ it also has gone back to the first level. Any ideas of problem I have?? I might also add that his game worked perfectly on my previous computer