Every Vehicle(loco wagon etc) has dependencies (bogey panto, product, corona etc etc)
-the first important fix, is get all dependencies complete
in CM right click, list dependencies recursively, a new CM window opens with a list
-next, each of these dependencies need not to be faulty for the main vehicle to work
if 1 is faulty, right click, View Error and Warnings like forester posted above
maybe just work to fix 1, so the process is clear, then repeat on the others
feel free to ask, greetings GM