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 ('a839f18fa25e0f08c61b44ca5174f28e', -1, 1397653505, 1397653505, '6ca2d26f', 2, 0, 0)

Line : 187
File : sessions.php