Running the installer throws error message, that does not seem to bother

The installer throws this exceptions, when doing a new installation, but also on update:

PHP Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /webs/ehlion.translate5.net/library/zend/Zend/Session.php on line 205
PHP Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /webs/ehlion.translate5.net/library/zend/Zend/Session.php on line 220
PHP Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /webs/ehlion.translate5.net/library/zend/Zend/Session.php on line 220
PHP Warning: ini_set(): Headers already sent. You cannot change the session module's ini settings at this time in /webs/ehlion.translate5.net/library/zend/Zend/Session.php on line 220