I just got a new intel 2.0ghz 17" iMac with built in isight. The videochat works with almost everyone on my buddylist but there are a few people that it doesn't work for. One example is a videochat with a buddy who i know has a new macbook with built in isight and has successfully videochatted many times before. and I have also had successful video chats with computers of this exact specification. Any advice?