I've been totally satisfied with running Ubuntu via WUBI ... except for Grub upgrades. I did
know to avoid them, but this last one seemed to imply that it was a fix
for the problem, rather than yet another manifestation of it.
For those who haven't seen it, upgrading Grub (or is it just Grub-pc?) blows up your ability to boot to Linux. My solution was to reinstall
Ubuntu (!), after copying my root.disk off to a separate file. Then, with a fresh, bootable OS, I mounted the old root.disk...