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 ('e5a223e2bcd4390bd151f421678790f0', -1, 1397632474, 1397632474, '6ca2d4d7', 23, 0, 0)

Line : 187
File : sessions.php