I've been using AF 5.7 for several months now. The last week or so, I'm finding that after several minutes of use, the frame rate starts dropping until the program becomes unusable (30 or below). I've tried restarting AF, quitting every other application, rebooting the computer, unplugging/replugging the USB adapter, all to no effect. Eventually the frame rate comes back for a while but I don't know what makes that happen. When it's slow, Activity Monitor shows no unusual processor use. Any suggestions?

MacBook Pro (2 years old), 8GB memory, OS 10.6.8.

Thanks.