how do i stop angry bots from crashing?

Hi, I am currently studying for a degree in sound production. One of my modules requires that i replace all game sounds in angry bots. I have changed the sounds in the assets folder but when i try to play the game it simply crashes after 5-10 seconds. I am running El Capitan (10.11.5). Most other kids in my class are experiencing the same issues. Please help as our assessment is due in in 4 days. many thanks in advance. alex