I installed Ubuntu 7.04 on a PC already running with WinXP.
Everything went OK but after restarting my system, I was unable to start WinXP from the Grub menu, I got the following error:

Error 24: Attempting to access block outside partition

My menu.lst file looks like this (not the complete file):

title Ubuntu 7.04
root (hd0,5)
kernel /boot/vmlinuz-2.6.20-15-generic root=UUID=968e649e-603e-4cd0-b7c1-6b8ec62d1333 ro quiet
splash
initrd /boot/initrd.img-2.6.20-15-generic
quiet
savedefault

title Ubuntu 7.04 (recovery mode)
root (hd0,5)
kernel /boot/vmlinuz-2.6.20-15-generic root=UUID=968e649e-603e-4cd0-b7c1-6b8ec62d1333 ro single
initrd /boot/initrd.img-2.6.20-15-generic

title Windows XP
root (hd0,0)
savedefault
makeactive
map (hd0) (hd1)
map (hd1) (hd0)
chainloader +1

Fdisk for sda looks like this:
Device Boot Start End Blocks Id System
/dev/sda1 * 1 2550 20482843+ 7 HPFS/NTFS
/dev/sda2 2551 19456 135797445 f W95 Ext'd (LBA)
/dev/sda5 2551 6374 30716248+ 7 HPFS/NTFS
/dev/sda6 6375 10198 30716248+ 83 Linux

As you can see, XP is installed on sda1 and Ubuntu on sda6.

Any help/suggestion is more than welcome since I'm stucked.

I think you might need to take out the "map" lines. Those are used when you have 2 or more hard drives to pretend that the second drive is the first drive (which many Windows versions require). Since it appears you only have one drive, you don't need it.

Thanks for the suggestion but it's not working: I commented out the two lines and I still get the same error message.

By the way, I also have an other drive (hdb) with other partitions (both for Win and for Linux) but it's not the primary drive used to boot the system.

I also forgot to mention that before using Ubuntu, I was using OpenSuse 10.2 and that the menu.lst used is (strangely) located on my previous OpenSuse partition: /media/sda9/boot/grub instead of /boot/grub.

Not a problem.....this presumably means that you did not install GRUB as part of the Ubuntu install---ie you are still using the GRUB that went with SUSE. The "gotcha" is that the GRUB file that goes in the MBR gets "hard-coded" to point to the correct /boot partition.

Your menu.lst file implies that Windows is on the first partition of the first drive---Is that correct? (Yes--I just looked at your fdisk output)

So--are you sure that the GRUB menu at startup matches the one you are editing?

Yes, I know that it's matching because the other menu.lst file (the one located in /boot/grub) looks totally different.

I also tried to compare with the menu.lst generated by the OpenSuse distribution but its structure looks completely different and it's therefore not helping.

Any suggestion is more than welcome since I'm totally stucked.

You can boot into Ubuntu and do the followingIf that doesn't work, you can try If you have SATA disks, use /dev/sda and setup (sda).

If you want to see where I got all this from, follow the link in my signature for Saikee's Grub Booting Tips.