Error updating sessions table

DEBUG MODE

SQL Error : 1062 Duplicate entry 'viewtopic.php?download=16198&f=21&t=1134&_f_=21x&_t_=1134x' for key 'session_page'

UPDATE phpbb_sessions SET session_time = 1774267560, session_start = 1774267560, session_page = 'viewtopic.php?download=16198&f=21&t=1134&_f_=21x&_t_=1134x' WHERE session_id = '51d45f297e6292c21e97916f994ab786'

Line : 556
File : sessions.php