can't log in to qantas frequent flyer on macbook air but can on iMac

Using safari on my macbook air: when logging in to qantas frequent flyer the window says logged in but keeps returning to the log in window and also I can't log out, this doesn't happen on my i Mac. I've rest safari with no result, I've rebooted also. When loogging in after reboot there is now no screen requiring password.