Unable to prevent user lockout

I help administrate an academic network and on one of our workstations any teacher who logs onto the machine will automatically be locked out as if they had locked the computer themselves after one minute of inactivity. We have tried to stop this from happening, but everything seems to be in order with regards to the screen saver properties as far as we can discern. This does not occur on student or admin accounts either which lead me to believe that the problem was something to do with an inherited group policy, however the problem only occurs on one workstation. We have found a temporary workaround in creating a new user account in a different user group, but it would be nice to be able to solve the problem once and for all. Any ideas?