Ok. I've learned how to solve an error that has been occurring to me lately, and I used the method on the SI3D 06 Toby, and the mesh is not a rendered mesh. It's just a shadow mesh. It does not appear in trainz AT ALL.
It's supposed to show toby in game. But, like I said, it does not. I did not build the model, SI3D did. This is what it says in the Errors and Warnings: Warning: This asset does not have a mesh that is visible by default.