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 ('de6fe40df6b70b1e0dbaf226b4ea46f5', -1, 1416761379, 1416761379, '365ba3e0', -1, 0, 0)

Line : 187
File : sessions.php