I’ve updated. The bug is still there. I got it fixed by putting into comment
<?php endif; echo "<!--"; do_action('topicmeta'); echo "-->"; ?>
I did that because I think that was around where the error occured.
bbPress version 0.9.0.4
PHP version 5.2.6
MySQL vesrion 5.0.67-community-log
Someone told me to change :
$this->rows_affected = mysql_affected_rows();
for :
$this->rows_affected = mysql_affected_rows($this->dbh);