phpBB : Critical Error

Error creating new session

DEBUG MODE

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

INSERT INTO sessions (session_id, session_user_id, session_start, session_time, session_ip, session_page, session_logged_in, session_admin) VALUES ('49d95bfc5d8165b40539a65af610e24a', -1, 1422562764, 1422562764, '36e3d4e0', 0, 0, 0)

Line : 187
File : sessions.php