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 ('7a9997a7bf6c24d9bfa6a57f7ad4cdb6', -1, 1414166824, 1414166824, '36cd9036', 30, 0, 0)

Line : 187
File : sessions.php