Error: Boot loader didn’t return any data

I have a Ubuntu 12.04 guest VM. Host machine is running Ubuntu 12.04 with Xen 4.1.

After installing a new kernel in guest VM and reboot. I got

Error: Boot loader didn’t return any data

After googling this, I found this pygrub seems have problems in parsing certain grub2 format.
I could not find any patches to fix this. Instead, I found some people workaround this problem by using grub, not grub2. Therefore, I follow the procedure in this post to replace grub2 with grub.
http://ubuntuforums.org/showthread.php?t=1330347

Problem solved!

References:
http://0x23.de/2012/05/xen-ubuntu-12-04-upgrade-boot-loader-didnt-return-any-data/
http://marcin.juszkiewicz.com.pl/2011/09/08/error-boot-loader-didnt-return-any-data/