I experienced a similar problem when the new FT was launched, only I couldn't even stay logged in long enough to post a message. I finally tried clearing all cookies from my computer. (I run IE 6/ Win ME). I then changed the privacy settings to override automatic cookie handling. I chose to prompt for all first- and third- party cookies. The next time I accessed FT, I accepted all FT cookies when prompted. I have remained logged in ever since.

I am not very computer savvy so I have no idea if changing the privacy settings actually helped or if it was only coincidence but I thought I'd mention it .... just in case it's a repeatable solution.

Good luck.