[Koha] koha requiring constant login/authentification

Hi, I have the problem that koha 1.2.3 requires authentification (login) on each new page of the librarian's module. One mouseclick, one login - impossible to use :-( I tried it with mozilla 1.4 and with IE6. Koha is installed on debian 3.0 i386, perl v5.6.1, Apache/1.3.26, mysql 4.0.13 Where should I look? What can I change to make koha require just one login per session? Greetings from Germany, Mat