Account LockOut in Windows 2000

A limited number of our users have two PC’s (one in the office and one at home) that they use for accessing the company systems. Whenever these users change their domain passwords from one of their PC’s their domain account suddently starts gettingdisabled. I keep enabling the accounts, but 10 minutes later I look in Active Directory User and Computers and see that the accounts have been disabled again. This only seems to happen to staff that access the system from multiple PC’s. Anyone have any ideas as to what could be causing this problem.