Error “This voicemail is in use” when attempting to access voicemail

In the NBX main menu on the server there will be an icon for NBX Messaging.

In NBX Messaging if you hit “Status” this will show you all the voicemails that are on hold or are being currently used. You should be able to click the name of the person’s voicemail you are trying to fix and hit RESET at the very bottom of the window.