[RCD] session problems

I've installed the roundcube 0.7 (freebsd port) into my machine, but I can't login with the system showing "Your session is invalid or expired."

In the session logs, whenerver I try to login I get a:

[05-Jan-2012 09:47:05 -0200]: Session authentication failed for hu51sq0hdvfhbe3u6eka8bj935; invalid auth cookie sent

Versions:

postgresql 9.0.5 with "timezone = 'America/Sao_Paulo'"; roundcube 0.7 with "$rcmail_config['timezone'] = 'America/Sao_Paulo';".

I've searched through the list, goggled, and found something about plugins, but i didn't enabled any plugin here (yet).

Is there anything I'm missing? Any clues? What can I do to help finding what is wrong?

TIA...