If you get an error with the mkinitrd command try it manualy. Adjust /boot/initrd.img-2.4.20-1-386-sec to the filename you entered in the lilo.conf. You have to adjust the /lib/modules/... and the root device after -r also.
mkinitrd -r /dev/hda3 -o /boot/initrd.img-2.4.20-1-386-sec /lib/modules/2.4.20-1-386-sec/
root
2018-05-08