Symptom
The scroll wheel on your third-party mouse, trackball, or other device does not respond after hot plugging.
Note: "Hot plugging" describes the capability of USB and FireWire devices to be plugged in and unplugged while the computer is turned on.
Note: You may only experience this issue on a computer that originally came with Mac OS 9.1.
Solution
Restart the computer to regain scroll wheel function.