NG15 backup drive 'Unavailable

NG15 - I want to delete a recovery point, but my backup drive (a 1 TB iomega, normal NTFS partition) always shows as 'Unavailable' in 'Manage Backup Destination'. But when I delete the recovery point using Explorer, NG opens up a 'Clean up recover point history' window that lets me remove the recovery points. I can live with this, but I would have thought after so long in production, weird bugs like this would be ironed out. Obviously I can backup to the drive OK.

But then again, maybe it's also something to do with the iomega drive as Windows Backup refuses to work with it at all!