Not able to add categories to a product

This weird problem just started happening out of the blue for me:

When I go to a product page and click the Links tab, I'm no longer able to add any new categories to the product. I will begin typing a category (i.e. "Bargain Shelf") and it will suggest the category via auto-fill, but when I click on it, nothing happens.

This is posing a big problem for me, because every week I switch up the products that are on my Bargain Shelf and send a newsletter to my subscribers. The way I make sure new products are rotating through is by temporarily adding "Bargain Shelf" as a category to the product, so they show up when you visit our Bargain Shelf page (http://onlineshop.yarniapdx.com/bargain-shelf--) on the site.

I am currently not able to add this category to any of my products, so I'm at a standstill with this. I have tried adding other categories just to try it out and the same problem happens. I've tried this in both Chrome and Internet Explorer.

Please help!

hi YarniaPDX,

Have you checked your error logs in opencart as well as the hosting server ?

What was the latest extension you installed ?
And I know it sounds silly but have you maybe update to a later sql server or php update ?
Or changed any of the file permissions.
You can also in chrome right click after you tried to add the category and select inspect element. You will see a error in the developer console that will at least guide you in the right direction.