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 ('21fba4eea4ac7d3d51f0fac4f3bb1fe5', -1, 1397623845, 1397623845, '6ca2d442', 19, 0, 0)

Line : 187
File : sessions.php