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 ('1e96d4ff64d72a1608f2dc38b62b5b8b', -1, 1414828727, 1414828727, '36a60f98', -1, 0, 0)

Line : 187
File : sessions.php