Ruby on Rails Delete Cookies For Remember Me

Ok, I have followed Ryan Bates' guide to adding in a remember me feature and everything was working fine.

I already had users in my database however and so when I tried to log in with them the system does not create an auth_token and so crashes, the problem I am now having is that because I attempted to log in it has stored the cookie so now whenever I open the system it crashes.

Can someone please help!!!