69702 Need a Foolproof Login System

I have a dating website that uses the AzDG platinum dating script. The script is written in PHP. It has a log-in system that uses either sessions or cookies depending on which option I have chosen from the admin area. My problem is that no matter which option I choose there are site members who report that they can't login. I have asked for help from AzDG and they made some updates, but I still get complaints from members. I've also obtained help from one programmer through scriptlance before on this issue. He was able to help some. Some members were able to log in after he helped us, but I still get complaints. What I want is for someone to provide me with a login system that will work for anyone and not be dependent on how members' computers are set up. Is this possible? Perhaps, the system could check for cookies, and if it fails, go to sessions and if that doesn't work maybe something else. I don't know. You tell me what will work.