Update, Error 500

Hi

I was trying to update Hikashop from 1.5 to 1.6, but was unsuccessfull.
The error message was this one:

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500 - An error has occurred.
JDatabaseMySQL::query: 1060 - Duplicate column name 'taxation_cumulative' SQL=ALTER IGNORE TABLE `jos_hikashop_taxation` ADD `taxation_cumulative` TINYINT NULL;

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Any hints what and where should I change to make Hikashop run again?
Thanks

Thanks. Soooo easy... )))