It looks like you're not the only one having this problem.
- First, make sure you are running the newest version of the operating system: Click on the Apple menu (blue apple, top left).
- Click "Software Update".
- Install new updates.
- If 10.4.7 doesn't fix it for you, unplug everything except the modem.
No luck? Ugh! Wait for Apple to fix it. You might try plugging it into a different USB slot, too. Be sure to call Apple. Maybe they have a fix.
Good luck.
Doug