native CI sessiosn problem

[eluser]new_igniter[/eluser]
Hello,
I really need some help and would love to get some basic advice. I am using the native CI_sessions, but am running into an odd problem. I have posted several times but have had no response, so any response at all is good.

Basically, when someone logs in, I give them the off the shelf ci_session cookie, nothing special, set to expire when the browser closes. The problem arises when 2 people, who each have an account, login from the same computer.

Overtime, the login just stops working and just sends them right back to the login screen..no errors in the log, no validation output, just refresh. This will continue until the cookies are cleared.

Has anyone experienced anything like this in the past?