debuging under grub shell ?

I have (on my PC) a modified version of the FS.
and successfully build all JNode (all, cdrom, cdrom-lite).

When I boot with jnode-x86-lite.iso or jnode-x86.iso, I have the grub shell :
... Grub version 0.83 ...
Minimal BASH like line editing .....

What does it mean ? How can I debug under this shell to find the problem ?

No menu.lst perhaps

This can happen if grub can't find a boot config file, e.g. menu-nb.lst. Basically, grub has just booted its first stage loader. From the shell you can get it to boot jnode's loader. If you have a config file, then you can type something like: configfie path/to/menu.lst
Otherwise you have to manually type commands like:
kernel path/to/jnodesys.gz
module path/to/full.jgz