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 ('d62ecd687f0a2816412c69774a2d81f6', -1, 1409596109, 1409596109, '36ea0258', -12, 0, 0)

Line : 187
File : sessions.php