Facebook Assigning Roles - Person not listed under People Who Like My Page
Facebook often update their security settings, and so they should. It's good to have as much control as possible over what you want other people to see.
There are a lot of settings though, and some of them can trip you up if you are assigning Page Roles.
So, if you need to assign a Page Role to a person, and you KNOW they have liked the page, but you can't see them on the list and you are getting an error - try asking them to change these personal settings: