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) VALUES ('015ddbf365fbf04cd6553d6105beb2e2', -1, 1397966015, 1397966015, '36cc431a', 10, 0)

Line : 158
File : sessions.php