Explorer error hangs on re-boot

I have a workstation running win9x. The user is to close their applications before ending their shift and simply log off of their workstation NOT shutdown. The user closes Outlook 2000 and SideKick and then selects ‘log off’ from the start menu. The system will not log off..instead it hangs with an error “Explorer has caused an error and will now close”. The system never logs off and the user needs to hold the power button in on the tower in order to restart the station.

What steps would you take to troubleshoot this issue?
Any help would be appreciated.