phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 'session_user_id'

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('73f0d92d1e323a1142580e722f5f0d44', -1, 1409429574, 1409429574, '36ea9fe5', -1, 0, 0)

Line : 187
File : sessions.php