Voicemail problems

I am using freepbx and when a extension is not online and you call the extension it says “an error has occur”. Or if the extension is registered and you let it right 3 times or so, it says the same thing “an error has occur”. I think there is a problem with my voicemail module. How do I fix this?

Our voice mail is not working. if you call extension it does not go to voice mail or when the extension is unregistered it does not go to voice mail.