The ISO filesystem which was generate by genisoimage (from cdrkit) was working on most systems, but few computers just refused to boot from this ISO image.

You can see messages from users who have been affected by this bug:
http://www.sysresccd.org/forums/viewtopic.php?t=2326

As a consequence, I just released SystemRescueCd-1.1.2 with a fix for that problem. The ISO filesystem is generated by mkisofs from cdrtools, and it works for everybody.