Loss of printers

I have a PII running WIN98SE with 128MB RAM. Frequently when running MAS90 and trying to print, the printer will stop working. If I go into the Printers folder, all three installed printers are gone. If I reboot the system the installed printers re-appear and the user can once again print from the MAS90 application; that is, until they disappear again. Sometimes the user can go all day without this problem and somedays the problem will occur several times. What’s happening and how can I solve the problem?