Oh hmm...that makes a little more sense I guess. Better Combat is a mod that allows you to attack with weapons in your off-hand. So I Guess maybe that's conflicting and not playing well with Quality Tools? Would it be possible for you to support Better Combat in order to avoid the crash with Quality Tools in the off-hand?
Ah. That makes sense. Did you tell the Better Combat mod maker about the crash? It has happening in their code, so I can't fix it from this mod.