Syslinux - Aug 2007 - Unable to boot from USB CD-ROM on AMD Geode LX800

I'm trying to build a bootable CD for an Advantech PCM-4153 board (based on
an AMD Geode LX800) that will allow to boot from USB CD-ROM drive.  I've
created an ISO that will load ISOLINUX (3.51) and appears to load the kernel
and initrd images, but reboots the system when it tries to run the kernel.

When I use either isolinux.bin and isolinux-debug.bin, the last messages I
see on screen are:

Loading kernel.......
Loading initrd..................
Ready.

I've enabled the %debug block in runkernel.inc (line 470) to wait for a key
to be pressed, and it does get to that point.

I've been able to successfully boot the same kernel and initrd images using
GRUB (via a network boot), I can boot my ISOLINUX ISO in a virtual
environment (Parallels on Mac), and I can also boot a Ubuntu LiveCD (
6.06is the version I happen to have around) from the USB CD-ROM on
this board.

Any ideas?

--Chris