Have you checked for missing dependencies? If a dependency is missing the locomotive will usually be a no-show.
In TRS2004 TrainzObjectz is the best utility for determining what might be missing.
Phil
Edit:
If it be the little 0-6-0 switcher, this has caused great wailing and gnashing of teeth, and made even grown men weep. You will find all the dependencies for this little gem by clicking here:
IC, I'm sorry, but please butt out when you don't know what your talking about. His question has been answered, and you then have come in with another answer that is NOT relevant...
Please, read the previous posts, and if the question has been answered, don't post
Zec