Most times it means the Family member you downloaded the app from has either made the purchase hidden, decided to stop sharing purchases or has left the family. Any of these will remove your access to the app and you will need to purchase it yourself. Also, the developer may decided to stop allowing the app to be shared.
The person you shared it from may need to check their settings if they are still part of the family.
http://support.apple.com/kb/TS5449