2nd hand copies of any game - especially if they have a serial number - are considered dead since the serial number was already used. Trainz has it once its used, its used and aren't transferrable, and that's what you are experiencing more likely.
And what oknotsen said, even if you were able to successfully register, you'll be required to get a FCT to access the DLS for older versions, as they're pretty much cut from the free DLS access.
Cheers