Closing a NoteBook that is no longer available

[Hip2Bsquare]

I have a notebook that has a file path associated with my old backup HD. I no longer have that backup drive but onenote still lists it to try and sync it. Unfortunately I cannot delete it (path doesn't exist) and I cannot close it as it is simply greyed out. It's just in my list and there seems to be no way to close or get rid of it. Any ideas?