Windows 98-GPF on Shutdown

We have updated numerous computers to Windows 98 Second Edition from Windows 95. On two systems we consistently get GPF’s and the blue screen of death on shutdown. We have discovered that this doesn’t happen if we just reboot the system and then immediately shutdown. It happens only after time and access to a variety of software–some of which are specialized programs. The problem is not consistent across all computers that have been upgraded that access the same bank of programs. Office 2000 is one of the programs loaded on these computers Does anyone have any suggestions on corrective steps? All suggestions are welcome!