This problem is officially known as the 'Great White Void' and occurs when heading West to East over certain routes. You could become Mr Technical and move the route accross various tiles but as Harold said, the easiest way is to save (press F2) and exit the scenario. You then have to choose the option in the main Train Simulator menu called 'Load Saved Activity' and select the one that you have just saved. The saved games are listed in date order.
You are using the NWE route from what I can see. This will therefore happen leaving Liverpool Lime Street, Southport and Ormskirk.