I kinda doubt this is a problem, those warnings aren't much of an issue, it'll finish loading without them. The main problem is the game loads *all* the portrait or body image files. For portraits, they tend to be smaller and so it'll be faster, but can still take a while and the game might run out of memory. For bodies, they're larger and with enough it's highly unlikely the game will ever finish loading them successfully, more likely it'll chug for a long while then crash.
Basically if the folder's not quite too big and you have enough memory, you can wait it out and it will eventually finish.
I started a mod to make it load things on-demand, I'll try and finish that up.