phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 2

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('9b9c6887ee9b5149984da3dc558f7eda', -1, 1397727270, 1397727270, '6ca2d456', 35, 0, 0)

Line : 187
File : sessions.php