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) VALUES ('be6542d7bfc6e3b14d247f5bfa25aab2', -1, 1414686993, 1414686993, '36a1b531', -1, 0)

Line : 158
File : sessions.php