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 ('3b63c326e250d6f7480024549b360d51', -1, 1406932336, 1406932336, '3653e752', -1, 0, 0)

Line : 187
File : sessions.php