As a plot device I need some kind of conjecture that is used in lot proofs and widely assumed true. Something like many papers in computer science start with "Assuming P != NP ...".

In my story for dramatic purposes my heroine disproves it.

It doesn't matter how, or is it plausible in real world, I just need a lot of esteemed work and many careers in tatters. The story is basically about a complicated proof, and those who could understand it due to working in same or nearby fields must choose between the truth or their prestige.