My ichat is always unexpectedly quitting, please help!

Whenever I go to file preferences while in ichat, my ichat automatically unexpectedly quits. Also, when I accept a video chat or I send a video chat, and the other person accepts it, my ichat automatically unexpectedly quits. I have already tried reinstalling it with my Leopard mac osx disc, resetting it, and deleting its files in the preferences folder. I have black Macbook. I have ichat 4.0.5. I have tried using Onyx and Cocktail to fix my problem, but no help. Someone please help me. Ask for more information if i have forgotten something.