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 ('0334d31d98189fb3f65a829ed6f10753', -1, 1414145696, 1414145696, '36c43e84', -1, 0, 0)

Line : 187
File : sessions.php