2.5升级4.1出现如下问题

运行 upgrade25to4.php
出现下面的提示,什么原因哦?

Discuz! info: MySQL Query Error

Time: 2006-7-27 11:59am
Script:

SQL: UPDATE cdb_settings SET variable='postbanperiods', value=REPLACE(value, ',', '
') WHERE variable='maintspans'
Error: Duplicate entry 'postbanperiods' for key 1
Errno.: 1062

Similar error report has beed dispatched to administrator before.