Why would you want wubi. It is now being discontinued. Also any abnormal shutdown may totally erase wubi as it is just a large file inside a NTFS formatted partition. Ok for testing but any long term use may lead to issues.
Why not use USB flash drive as a persistent install or if larger a full install?
wubi direct boot where hd0 is boot drive, yours should be different, and it is in partition 2 which may als be different. So both hd0,2 and sda2 must change. May be sdb1 and hd1,1 if you only have one other drive. Boot drive is always hd0, but other drives usually are in BIOS order.
Not sure if this works when inside Windows or not. More to boot wubi when in its own partition.
menuentry "Wubi" {
insmod ntfs
set root=(hd0,2)
loopback loop0 /ubuntu/disks/root.disk
set root=(loop0)
linux /vmlinuz root=/dev/sda2 loop=/ubuntu/disks/root.disk ro quiet splash
initrd /initrd.img
}
Really old info on caveats:
Posts by meierfra. to use grub2 to directly boot wubi
http://ubuntuforums.org/showthread.php?p=8903013