CSRF token problem with CodeIgniter

I am having a very weird CSRF protection problem in CodeIgniter. I have made sure that I use form_open to start my form, csrf_protection is set to true in the config file, and I have also made sure that the hidden csrf name and value fields match the csrf cookie as seen here: http://d.pr/3cfB.

What happens is that when I submit the form, I get "An Error Was Encountered. The action you have requested is not allowed." error and am not sure why. The form works fine when I turn the csrf_protection off.

What's even weirder is that I use tank_auth library for my authentication and it also uses form_open for the login form. I did check to make sure that there is a hidden csrf field in the login form when csrf_protection is on and I was able to submit the form and log in with no problem.

Thoughts on what I can do to debug this problem?