The Problem:

Recently, one of our clients wanted to change the slug, or permalink, from “about-2″, back to just plain ol’ “about”.  I tried changing the slug from the “quick edit” mode. I tried to Edit the Permalink from the Post Page. No luck, it kept reverting back to about-2.  After doing a few searches, I noticed that others had experienced this problem as well.

The Solution:

So, I finally found this post on the WordPress support forum which suggested I check the Trash folder. Sure enough, I found a page called “About” hanging out in the Trash. Once I permanently deleted the page from the Trash, I was able to save the permalink successfully.