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 ('5a0d3d7cc55a71f3d26f77462e022b8d', -1, 1397653510, 1397653510, '6ca2d26f', -4, 0, 0)

Line : 187
File : sessions.php