Welcome to the Forums.
I wish you luck on your challenge. It may be a glitch or maybe the guide is wrong? I can't really recall exactly where locations are to help you, I'd know them by sight.
At Anyrate I am sure you will succeed, you sound like a capable sort. Tell me, are you a capable sort?
When in doubt, replay from the latest save and try again.
Check this walkthrough from gamebanshee
maybe this will help.