Error with Windows 2000

A user is trying to register for a class using one of my forms. He says:

It gives me an Windows error when I click on any of the check boxes. Then sends me to the website.

Seems to be a Windows 2000 thing. I was able to complete and submit the form on a Windows XP machine. Windows Internet Explorer in both cases. On the Windows 2000 machine, ZoneAlarm firewall with popup blocker and mobile code blocker both turned off.

The link to the form is here:

https://secure.rigpaus.org/secure/Courses/DLP_LovingKindness.html

I have shared it with support.