It appears that you left out several steps in the "chrooting" section. Go back and read the link posted earlier. You need to use all the steps to gain access. Unless you did them and just didn't post them all?? Also, you're using LVM so I would expect sdb1 is the /boot partition not the root partition so you might need to change the command to reflect that.
You might google "bootinfoscript" and go to its site, read the instructions, download and run it. It will contain detailed information on your drives/partitions and boot files. If you can't resolve this, posting its results.txt file here should give enough details for someone to explain what you need to do.