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 ('cb3035a5a158510297ddb2fd4cb9c3a0', -1, 1405347992, 1405347992, '36c46ce8', 37, 0, 0)

Line : 180
File : sessions.php