another thing you could say is that if your comp doesnt have enough RAM or hard drive memory it cant process it all at one time. in other words, my comp sometimes says that i cannot place an animal because i dont have enough hard drive memory. it needs memory to run the game! also if thats not it, your comp is experiencing RAM probs and it cant run it all at one time, so it doesnt run or include some files. or maybe if u have usermade downloads they r interfering w/ the game or game files.
hope this helps!!=)
:flipper:
(and it could be very simple...your animals are dying lyke pokefan said)