Category doesn't show up under product links tab

I created a category and I noticed this particular category is the only category that appears on a second page. It's the 21st category I've created. The other 20 all show up on one page.
I'm attempting to now add a product. I filled out the info under the general tab, I then filled out the info under the data tab, now I'm filling out the info under the Links tab. When I click in the Categories box to select the category I created under the category option it doesn't show up. I show the other 20 categories I previously created but it will not show this 21st category I created. Any help as to why this isn't showing up would be great.

You need to always fully clean out your OcMod / VqMod / System Cache Sections,
as well as the Browser Cache, before you can see changes made.
Ernie

Didn't work. What I did notice was that I created another category with a sort number of zero and that shows up. However, the 21st category does not show up now. This tells me that somewhere in opencart there is a setting that allows you to set the limit of categories to be shown. Right now it will only show 20 and no more. How do I get the 21st category to show?