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 ('abd1591678b48959628162dea913fa6b', -1, 1436100497, 1436100497, '17140917', -1, 0, 0)

Line : 187
File : sessions.php