I just got this problem on firefox. I can see the threads but clicking any of them will get to an error page. So I went in and deleted all cookies related to flyertalk.com and now everything works just fine.

On firefox, go into options -> privacy -> remove individual cookies
type in flyertalk and select all the ones with flyertalk in it.. and click remove selected. Exit browser, go back in and log back into the flyertalk forum.