Hmm...seems like there are no takers. But then again, ant bully isn't known to be a problematic game. I suggest you experiment a bit with the settings. Is there an alt dol on the disc (if so: use it). Try loading it with other cIOS'es. Most work on Waninkoko's rev21 base IOS 56, but you can try using 57 or 58. Or even hermes's cios'es 222, 223 or 224.
What is the cIOS you're currently using? And perhaps most important: do your other games work fine?