Good Morning Jd_James
I would recommend that you run an extended database repair, as it appears that some of the required assets are not being located by Trainz.
To run an extended database repair, please click on the 'content' button on the launcher screen to launch Content Manager. Once Content Manager has loaded, please click on 'file', then on 'extended database repair'. Once the database repair is complete, close Content Manager then try running Trainz again.
If you are running Windows Vista, Windows 7, or Windows 8 then please also ensure that you have set the 'Trainz.exe' file (in the TS12 folder), and the ContentManager.exe, TADDaemon.exe, and TrainzUtil.exe files (in the 'bin' folder, within the TS12 folder) to run as administrator.
Regards