upgrade database from 1.6 to 1.8 problem

[Gillesvdb]

Hi,

I'm upgrading my zabbix from 1.6.4 to 1.8.2.

Now, I'm trying to upgrade my database with " cd mysql; mysql zabbix -u zabbix -p < patch.sql"
I found the command on the manual pages on Zabbix.com

When I try this, an error occurs: ERROR 1060 (42S21) at line 1: Duplicate column name 'esc_period'

What is the cause of this problem, and how can I solve this?

thanks!