Error updating sessions table

DEBUG MODE

SQL Error : 1062 Duplicate entry 'viewtopic.php?download=18784&f=26&t=1287&_f_=26x&_t_=1287x' for key 'session_page'

UPDATE phpbb_sessions SET session_time = 1788990901, session_start = 1788990901, session_page = 'viewtopic.php?download=18784&f=26&t=1287&_f_=26x&_t_=1287x' WHERE session_id = 'bee14f2ca7d02822b0451f25a936a304'

Line : 556
File : sessions.php