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 ('8b3bab52c578ea8869f4896d22858850', -1, 1397644024, 1397644024, '6ca2d4f5', 26, 0, 0)

Line : 187
File : sessions.php