When starting the ubuntu with GRUB, that display some error below:
error: invalid environment block
Failed to boot default entries.
Press any key to continue...
Here is the way to fix the bug.
1. Make sure that you have a live cd in your hand.
2. Boot the computer, under the fixed model, insert the code below:
cd /boot/grub
rm grubenv
grub-editenv grubenv create
grub-editenv grubenv set default=0
3. Now you can check whether the option is ok.
grub-editenv grubenv list
That will display:
default=0
Since then, we fix the bug! Reboot the computer, and...
Have fun!