I take it this is a new installation ?
Did you turn off your antivirus when installing Trainz ?
After installation have you made "Allowable Program Exception Rules" in you antivirus program, to "Always Allow" Trainz launcher, and Trainz CM through ?
Right click on the Trainz desktop launcher icon, and click properties/advanced, and tick the box "Run As Administrator"
Have you patched TS12 to a higher SP (even I am confused by the Patch page, it is very unclear on what to patch to, as there are no instructions on what patch's to apply).
And you are not suposed to run Trainz until it is patched (which could take 3 or more days of progressive patching, with your antivirus turned off (best done overnight as some patch's take @ 16 hours).
Sometimes this requires uninstall Trainz, restart PC, and re-install Trainz fresh.
When you first started Trainz, what build numeral was showing in the lower corner ?