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 ('c97d7d8babb60faa3574be91e1b06a72', -1, 1414033172, 1414033172, '36a354c7', 0, 0, 0)

Line : 373
File : sessions.php