SQL-DATABASE ERROR

Database error in Woltlab Burning Board (2.3.6): Invalid SQL: SELECT COUNT(threadid) FROM bb2_threads WHERE boardid='115' AND important < 2 AND visible = 1
MySQL error: Unknown column 'visible' in 'where clause'
MySQL error number: 1054
MySQL version: 5.5.21-55
PHP version: 5.3.13
Date: 20.05.2012 @ 12:05
Script: /BB/archive/115/board.html
Referer: