Error 25: Disk read error

[John Kelly]

I start grub from a floppy, with two menu entries; the 1st looks for
grub on the hard drive, and the 2nd is a fallback in case grub is not
found on the hard drive.

Works great using a floppy, but now I need to use a CD instead of a
floppy, and the fallback does not work when using the CD.

After reporting the first error because grub is not found on the hard
drive, it tries to run the fallback entry, but fails, reporting:

  Error 25: Disk read error

and will not run the fallback entry.

It looks as though some variable is not getting reset, because once
you get into this failure mode, you can't escape it, even with human
intervention, and you have to reboot.

I'm looking at the code to see where the problem is, but it's not easy
for a newbie ... if anyone has hints, they would be welcome.  :-)

BTW, if I make a floppy image and burn it to CD in floppy emulation
mode, it works fine, just like the real floppy does.  So the problem
is specific to the non emulation mode CD.