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 ('91b91319e97f775a6340cce45dfc74ab', -1, 1432632554, 1432632554, '36c57474', -1, 0, 0)

Line : 187
File : sessions.php