Sounds like you are having a similar problem to me.
I have had it since starting the board just a few days ago, and I use firefox.
I have to log in twice to get to the control panel. Then I am sent to relog in again often, from 2-10 minute intervals. This goes on continually. I can log in 20 times a day while setting this board up. VERY annoying.
I have clicked keep me logged in, and remember password, but neither work.
I think it is something to do with:
Session length, Sessions will expire after this time, in seconds. Mine is set to 0, but I don't know how many seconds is the best to set it for.
Also there is a log in expiration length in days in general/security settings for the person who was looking for it.