I haven't seen this problem on a Win98 PC, but I have seen it on WinNT and Win2K PCs at my place. There are several things you could try, but these are untested on Win98...again since I have experience with NT/2K only, I don't know how well it will work with Win9x. (Use with caution)
1. I believe there was a hotfix that included the functionality to request a full properties retrieval when performing an Agent Wakeup Call. Give that a try.
2. If your Agent Wakeup Call doesn't have that option, you can always do it manually by deleting the FULLPROPS.INI and restart the PC to have the ePO Agent repopulate the file.
3. The other thing you can do is uninstall the ePO Agent, uninstall VirusScan, reboot, edit the Registry and remove the entries for Network Associates where it refers to ePolicy Orchestrator and VirusScan, reboot, reinstall VirusScan, then reinstall ePO Agent.
Good luck!