I have the same problem. I can log in, then FA asks me to login again after I click on anything. I already tried setting the php5.ini to redirect the temp folder, i can see the temporary files being generated. I modified the session file as well (uncommented). I'm fresh out of ideas.
Had the same problem. Then I downgraded PHP from 5.3 to 5.2 and everything was ok.
Moj