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 ('47cf6c0b9e8360c3a83ad2ea1c4bbbbc', -1, 1246863820, 1246863820, '26673f3a', 0, 0, 0)

Line : 189
File : sessions.php