phpBB : Critical Error

Error creating new session

DEBUG MODE

SQL Error : 1062 Duplicate entry '-1' for key 2

INSERT INTO phpbb_sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('bec1a634b1114f0ddbaa649b9aae8b10', -1, 1425280020, 1425280020, '36d3b6f1', 20, 0, 0)

Line : 187
File : sessions.php