Error: unknown filesystem.
grub rescue>

grub rescue>ls (hd0) (hd0,msdos5) (hd0,msdos1)
grub rescue>ls (hd0,msdos5) unknown filesystem
grub rescue>ls (hd0,msdos1) unknown filesystem
grub rescue>ls (hd0) unknown filesystem

ls                               # List the known drives (hdX) and partitions (hdX,Y)
ls (hdX,Y)/                      # List the contents of the partition's root
ls (hdX,Y)/boot/grub             # Normal location of the Grub 2 modules.
ls (hdX,Y)/usr/lib/grub/i386-pc  # Alternate location of the Grub 2 modules.

set prefix=(hdX,Y)/<path to modules>

set prefix=(hd0,5)/boot/grub
set prefix=(hd1,1)/usr/lib/grub/i386-pc

insmod linux
insmod loopback
insmod iso9660
insmod fat        # If ISO is located on fat16 or fat32 formatted partition.
insmod ntfs       # If ISO is located on an NTFS formatted partition.
insmod nftscomp   # If NTFS compression is used on the partition. Load if you aren't sure.

loopback loop (hdX,Y)/<path to ISO>/<ISO-name.iso>

loopback loop (hd1,1)/path/to/ubuntu-10.04.1-desktop-i386.iso

set root=(loop)
linux /casper/vmlinuz boot=casper iso-scan/filename=/<ISO-name.iso> noprompt noeject
initrd /casper/initrd.lz

linux /casper/vmlinuz boot=casper iso-scan/filename=/ubuntu-10.04.1-desktop-i386.iso
linux /casper/vmlinuz boot=casper iso-scan/filename=/my-iso/ubuntu-10.04.1-desktop-i386.iso

boot

/dev/sda1: LABEL="Windows XP" UUID="96A4390DA438F0FB" TYPE="ntfs"
/dev/sda3: LABEL="Ubuntu 11.04" UUID="b61fcae3-7744-45b4-95b9-7528d50a3652" TYPE="ext4"
/dev/sda5: LABEL="Se7en" UUID="A2DC9D71DC9D4109" TYPE="ntfs"
/dev/sda6: LABEL="Development" UUID="DEB455A1B4557CC9" TYPE="ntfs"
/dev/sda7: LABEL="EXTRA" UUID="D8A04109A040F014" TYPE="ntfs"
/dev/sda8: LABEL="SONG" UUID="46080FCD080FBAC7" TYPE="ntfs"
/dev/sda9: LABEL="BACKUPS" UUID="766E-BC99" TYPE="vfat"

grub rescue> set prefix=(hd0,6)/boot/grub
grub rescue> insmod normal
grub rescue> normal

sudo grub-install --root-directory=/mnt --boot-directory=/mnt/boot /dev/sda