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 ('c7f9c5fc4e57d6c9c5adb8b73c930c15', -1, 1280443330, 1280443330, '266bbf54', 15, 0, 0)

Line : 187
File : sessions.php