The most likely cause is that a Process is not terminating when you logoff that user. Using Task Manager check which processes are active just prior to logoff and see if there is anything there that may indicate a problem.
As an aside..... It is very bad practice to have 4 Administrators on an XP PC. While logged-in as an Administrator your PC is at more risk. Good practice is to have a single Administrator account and then User Accounts. Only login to the Administrator account when you have "Admin" things to do, and then logout and go back to a limited User Account for normal activities.