Arch won't boot after switching to ext4

Question

Hi,
Yesteday I converted my partition to ext4 sucesfully, and I managed to boot once after that, but when I tried to reboot, GRUB2 would say:
error: invalid magic number
while trying to load the kernel. I already chrooted from my Ubuntu partition and tried to fix by reinstalling kernel and fsck'ing, but no luck. ideas? I can't even boot from fallback :S

Answer 1

Ok, here's my grub.cfg
# Config file for GRUB2 - The GNU GRand Unified Bootloader
# /boot/grub/grub.cfg
# DEVICE NAME CONVERSIONS
# Linux Grub
# /dev/fd0 (fd0)
# /dev/sda (hd0)
# /dev/sdb2 (hd1,2)
# /dev/sda3 (hd0,3)
# Timeout for menu
set timeout=5
# Set default boot entry as Entry 0
set default=0
#Colors
set menu_color_normal=light-blue/black
set menu_color_highlight=light-cyan/blue
#modules insert
insmod linux
# (0) Arch Linux
menuentry "Arch Linux" {
set root=(hd0,5)
linux /boot/vmlinuz26 root=/dev/sda5 rootfstype=ext4 ro quiet
initrd /boot/kernel26.img
# (1) Arch Linux recovery
menuentry "Arch Linux Fallback" {
set root=(hd0,5)
linux /boot/vmlinuz26 root=/dev/sda5 ro quiet
initrd /boot/kernel26-fallback.img
menuentry "Kubuntu 8.10, kernel 2.6.27-7-generic" {
set root=(hd1,5)
linux /boot/vmlinuz-2.6.28-4-generic root=/dev/sdb5 ro quiet splash
initrd /boot/initrd.img-2.6.28-4-generic
menuentry "Kubuntu 8.10, kernel 2.6.27-7-generic (recovery)" {
set root=(hd1,5)
linux /boot/vmlinuz-2.6.28-4-generic root=/dev/hda1 ro single
initrd /boot/initrd.img-2.6.28-4-generic
## (1) Windows
#menuentry "Windows" {
#set root=(hd0,3)
#chainloader +1
BTW, if I change "linux" command for "multiboot", I get this:
alloc magic is broken at 0x19710
Any ideas on what may be causing this? Perhaps changing to GRUB-legacy would help?