How are time changes stored?

On a laptop running Windows 2000, I recently changed the computer time to the correct value. Since then, a 3rd party program fails to start, displaying an error message “The time on this computer has been changed” This particular program requires a password for access: after entering this (correctly) the system hangs for approx 20 seconds, with the hard disk LED illuminated, before displaying the error message.
Other people in the company have had to do a reformat, and reload all their software programs.
As I want to avoid this, can anyone tell me where in the registry any change of time is stored?