This might sound stupid, but do you have any other programs running in the background or things that launch at startup? Have you installed any software on it recently?
FartinMowler, I suggest formatting your computer. When you start getting illegal operations in Win98, the best thing to do is reboot because after one error like that, the system becomes unstable and more will surely follow. If you're contstantly getting them just start fresh with a nice format.
