Two things. First, make sure you've done the 'fix' at the top of this forum. Second, in Terminal, run:
Code:
sudo bless --folder "/Volumes/your-backup-volume/System/Library/CoreServices" --bootinfo --bootefi
substituting your volume name appropriately. Press Return at the end of the line, type your password (which will be invisible) and press Return again. Then try booting.