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 ('1b5af2a6b0a8ad79c83ee8c179db54e6', -1, 1419044149, 1419044149, '36e3d78c', -1, 0, 0)

Line : 187
File : sessions.php