Backup your site before you install this.
I'm sorry to hear Kunena caused a problem. It's imperative when trying a new extension to always backup your site. What you reported is first time I've heard of something like that. Did you try looking for help in our forums? Did you use the latest stable release? Frankly, with the little amount of info you given, it's very hard for us to believe this was Kunena's fault since it's the first time we've hear about issue like this.