Can not add new categories while posting

I installed this plugin today to better manage the way my categories are displayed. Now, I get a permissions error (You do not have permission to do that.) when I attempt to create a new category (in this case a sub category) while writing a post. I was able to go into my Dashboard > Posts > Categories and create it that way, but I am use to being able to do this on the fly whilst posting (though rare that I do this).

http://blog.ffextensionguru.com

https://ww.wp.xz.cn/plugins/collapsing-categories/