AS dermmy sugests, Install sp1 if you have to.Also
1 clich the radio icon everyyime you see it come on.Will save you much nail biting.
2 The message will most likely be.Junction missing a lever or no path to selected destination
If 1 find the offending junction It may not even be on the route you want to travel.
If 2 then run the train manually and see if it derails.You have a track break
These sometimes are very hard to find. You could also have double clicked a spline when laying track and have layered one small peice of track over another. look for mismached spline circles. Hope that helps
baz66