If you have phpMyAdmin open it. And then open the database, where the database tables of your Kunena Forum installation are.
Click on the left side on jos_fb_categories.
ON the right side above click on SQL and you will see a input textfield, where you can insert code. Delete the existing code in this Textfield
SET `locked`= 1
and click on OK.
This will lock all forums and categories.
To unlock all again insert this:
SET `locked`= 0
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