Comment 5 for bug 682337

Normally this problem is only associated with wubi installs on the same partition as windows. However, on wubi installs to a different partition/drive, they are susceptible to overwriting their MBR (bug 610898). If this happens, and they repair it, then they are susceptible to this same problem as this bug, after a subsequent "update-grub" e.g. from a kernel update.
The after the fact fix is the same as described above - boot ubuntu through manual grub.cfg workaround and then clean up /boot/grub and regenerate update-grub.