Ok, I'll have a look into that. Am I looking for game textures or unit ones? I've not done much with unit textures for the new faction yet, so I'm inclined to the former. I've left unit textures until later for the other factions I've added and other than being invisible, they've worked okay.
EDIT: since I have a working mod, and a non-working mod, both of which use the same base game folder, logically, all the files in there should be working correctly, right? Presumably, then, it's only the files in the mod folder that are actually wrong in some way
Update:
I've got error logging working now (yay), and the main error it's giving me for this is 15:12:26.031 [data.invalid] [error] Insufficient video memory to load requested texture set.
Looks like you were right, though I've yet to work out which textures and where they are.