I have just taken over a site for a client which is built on CI by a previous company which I have never dealt with before - Once I uploaded to my server and got the site running the admin side did not allow me to log in anymore. It can tell I am a user with the correct credentials but it just redirects back on itself to the login page again.
Any help or advice would be appreciated and I am sorry for the vagueness with the information but I am a total novice with this.
This sounds like a session misconfiguration.
Have you checked your session and cookie settings in config/config.php?
Specially cookie_domain, cookie_secure or any setting that may restrict session access.