This sounds like either a switch is not set, there is a train ahead of you that you cannot see, or you have a break in the rail, the way to solve this, is to manually drive your train past the red signal and see how far it gets, before derailing or bumping into another train.
I don't know if this works, but it used to work in Trainz 2004 and trainz 2006, if you move your mouse curser over your signal, it'll tell you what is wrong, and if you click on the signal, it'll take you to what is wrong...
Hope this helps
Joe Airtime
