If you edited an asset with CCP it changes the name of the folder
containing the alpha files. Not sure why it does it, I just know it
manages to do it.
If you read the Jetlog.txt file in the Trainz folder it will confirm this.
My experience has it this way. Edit the asset with "Edit in Explorer"
You will see the asset file tree. The names in your file tree will likely
differ from mine but the general discription will be
mesh_alpha_numbers
mesh_body
mesh_shadow
Change the name of the mesh_alpha_numbers folder to
_alpha_numbers
The means simply deleting the "mesh" from the file name. Leave
the leading underscore. Recommit the asset and try it.
The Jetlog.txt will tell you exacly what it was looking for name wise and
didn't find. So far this has worked for me every time, but I do check
the Jetlog frequently for assurance. I have yet to loose ARN capability
after using the CCP but it does require some editing.
Good luck!