Cannot find win.com

During boot-up, right after executing autoexec.bat I get an message that it couldn’t find win.com and therefore couldn’t start windows. But when I then manualy type in the location for win.com, the PC boots up.
Machine is running on Win98SE. Programs suchs as Norton Windoctor, DrWatson, Scandisc and SFC didn’t find anything suspicious.
Any ideas, anybody?
Thanks,
Vahur