Game crashes after you accept any trade offer by AIs. You can modify it all you want, does not matter - if you accept it, you are screwed.
Workaround: you can cancel trade offer, it will put you into the diplomacy screen with chosen AI.
Re-enter negotiation and modify deal now as much as you want.
How to: wait for trade offer, press accept, enjoy your crash.
Can provide DXdiag and other stuff if required.