Bill,

Good question! Wish I had a good answer for 'ya! [Linked Image]

As you know, the mouse movement thru the ball makes two Opto-Isolators pulse on/off.
This is done by passing a "Shade" through the light source, so it creates the needed 0/1/0/1 pulses. They get fed to the logic gates in the mouse, which turn out the serial bit streams to the mouse's serial port [resulting in Bytes and parity bits].

Ambient light may have the possiblility of interfering with the opto-isolators, but it would need to be the Infrared frequency used with the LED on the isolator.

I am thinking it's more of a driver [software driver] conflict than any light interference.
Could be a combination of driver and IRQ conflicts.
Is there any fault dialog boxes that accompany the problem [GPF, etc]??
Also, does it effect anything else??
If the problem is predictable - that is you can make it happen at the same time more than once, it is probably a driver/hardware conflict.
It being a scroll mouse might be throwing your machine into a tizzy with the scroll wheel's code. Check to see if the software and proper drivers for the scroll mouse have been installed and configured.
Also, the scroll mouse utility should have user dependent settings, which you could alter to correct this problem.
If all else fails, consider stepping back to a simple 2 button mouse.
FYI - try using a known good 2 button simple mouse as a test to see if it works properly. If it faults too, it's likely that the onboard mouse is not being disabled.

You could create a boot setup that disables any local [built-in] mouse and driver, when you plan to use the externally connected mouse [I also can't stand the mouse on a laptop PC and only use an external mouse, connected to the PS/2 port!].

Also, if you have about 10 hours to kill [Linked Image], dive into a conflict search [oh man that hurts, even to type it out!!!].

Does the problem also cause problems with the CPU and/or operating system - such as driven to snail speed, or locking up system - requiring a warm reboot. If yes to any of these, it's definitely a hardware conflict - like two items using one IRQ at once!!

What I thought Virgil was getting at might have been the cordless mouse??? [I am probably wrong]. But after re-reading his post, it's clear that he is referring to the "Optical" mouse [w/o a tracking ball]. Seen a few used by friends and clients, and they worked well under various light conditions.

Well, good luck Bill on the mouse thing! Let us know the outcome.
I'm thinking conflict, but could be interference from light entering it like you said. Only one way to find out... and I'm sure you know what that is [Linked Image]

Scott SET

Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!