Comment 76 for bug 477104

Type the next script in order to find the "Y":
grub>ls (hdX,Y)

where Y=1 in most of Wubi cases, hence>
...root=/dev/sda1
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grub>ls
grub>ls (hdX,Y) #find ubuntu partition
grub>insmod ntfs #load ntfs module
grub>set root=(hdX,Y)
grub>ls $Boot #find BOOT partition's UUID
grub>search --no-floppy --fs-uuid --set UUID
grub>loopback loop0 /ubuntu/disks/root.disk
grub>set root=(loop0) #reset loop to loop0
grub>linux /boot/vmlinuzxxxxxxxxx root=/dev/sda1 loop=/ubuntu/disks/root.disk ro quiet splash #load kernel
grub>initrd /boot/initrd.imgxxxxxxxxxxxx
grub>boot

after login, run “update-grub2” in terminal

Note: Use tab to complete xxxxxxxx

http://ubuntuforums.org/showthread.php?p=8471343#post8471343