It's a problem that can be worked around by amending the model. For some reason, and maybe only on some systems, it needs 8-character filenames for textures even though the names of the textures we paint are longer. I resolved a similar problem with Todd's Skymaster (for someone else's FS9 conversion) by opening the MDL file in a hex editor, finding the texture name, and reducing it to 8 characters.
I can't quite recall what the original texture name in the model was, I think it was probably "skymas~1", which is standard Windows procedure for working with longer file names. I fixed it by changing "skymas~1" to "skymastr" using the hex editor. I then altered all the original Skymaster texture names to Skymastr as well, "Skymastr.bmp". The lightmaps have longer names (_L at the end), but they work okay (well, I heard nothing back, so I assume they do).
You could try that with the Aztec. Is it a conversion?
I'm not sure why Todd's models have this quirk when no others do, as far as I'm aware.
So, use a Hex Editor to open the model, look for the filename, and see whether it ends "~1". If so, and for simplicity's sake, change it to something that fits the existing filename in length, which will be 8 characters. So, not "Aztec" but possibly "TB_Aztec". Then change all the texture names.
If it doesn't end with those characters, it will be some other problem that needs to be investigated. Life's full of challenges.
