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 ('03e8a8b664f69bbd4af38e4aee5faaab', -1, 1411040328, 1411040328, '365245be', -1, 0, 0)

Line : 187
File : sessions.php