Maybe you should tell us more about your setup and why you are getting these
notices. How many drives? How many partitions? How many OSes? Did you
install anything since you installed Ubuntu and have you removed any
devices? The more info you provide, the quicker we generally reach a
solution.

BTW, read the help documentation on Grub2 and it tells you how to re-write
grub from the Live CD. You want section 11 in the right hand menu.

https://help.ubuntu.com/community/Grub2