When trying to create a Pretty Link with mydomain.com/facebook, Pretty Link says
"ERROR: This Pretty Link Slug is already taken. Check to make sure it isn't being used by another pretty link, post, page, category or tag slug. If none of these are true then check to see that this slug isn't the name of a file in the root folder of your wordpress install."
WP Engine (my host) and I have checked all of the above. They've even checked the usual databases but can't find the problem. If I create a page or post with that slug, there's no problem.
I MIGHT have previous created a Pretty Link with that slug, and then I either deleted it or it disappeared.
Is there another database that we should be looking into?