Another thing to check: If you are using passenger stations, check that they are actually connected to the rest of the track. There should be orange circles at each end (or sometimes just one end) of the station for each platform. If the circle(s) is/are white not orange (the circles 'attached' to the station) try moving it a bit (the track, not the station) - if it moves, connect it to the white circle at the end of the station platform, it should go orange which means it is connected OK.
This happens quite a lot with AJS stations, and sometimes with other stations, if the track was not connected correctly or the station was put in after the track.
As said above, also check for rogue junctions (no green arrows) and cross junctions (2 diverging tracks in opposite directions connecting to the same spline point). Direction markers can also cause problems - if you are running a single line, don't use direction markers (the yellow ones) unless you are using passing loops.
I am also able to check your route for you if you want - PM me if you want my email address
Shane