Sounds like a CSP problem. I've noticed when I modded P:M that it's SUPER-picky about the EXACT size of the file.(e.g. If the one already in the brres is 64 KB, then it may be picky if you have a picture that takes up 63 or 65 KB of space; note: this is just an example, so it may not be THAT picky, as well as the exact size may vary) So try editing the CSP in MS Paint, deleting small parts of the picture, until the size is the same as the P:M one, and this should fix it. Cause I had a similar CSS freezing problem before I did this with mine.
Sorry I'm extremely late on this reply, but I had to ask about the CSP crashing you tried helping me with.
So I had an original mod for Snake with CSPs and everything which worked. I replaced the model and the CSPs with something else, and now the game crashes when I try to choose Snake. So then, I put back the model and CSPs to the ones that worked before, but it STILL crashes! What should I do?