Ok.

My two instalations were 'http://bevo' (on a local server). I changed the 'baseurl' (at '_config.php') to 'http://www.b2evo' (appart from changin 'httpd.conf' and '/etc/hosts').

The reason was a 'www.' problem related with cookies.

More at:
http://forums.b2evolution.net/viewtopic.php?t=4453