Well, I found the solution.
I use JForum with IAS 10gR3 for
servlet container and Oracle for Database.
In fact the oracle.sql was misconfigured in 2.1.7 version with the TopicModel.notifyUsers SQL text.
It must be
TopicModel.notifyUsers = SELECT u.user_id AS user_id, u.username AS username, \
u.user_lang AS user_lang, u.user_email AS user_email, u.user_notify_text AS user_notify_text \
FROM jforum_topics_watch tw, jforum_users u \
WHERE tw.user_id = u.user_id AND \
tw.topic_id = ? \
AND tw.is_read = 1 \
AND u.user_id NOT IN ( ?, ? )
[originally posted on jforum.net by sburky]