I experience failures like this with Time Machine every couple of months. The only thing to do is wipe the previous backup and start anew. This happens on all my Macs so it&#x27;s not device specific nor is it related to the underlying backup medium which is working perfectly. If you absolutely cannot take even the smallest chance of losing your data, TM is not a good choice. If you need something that runs for years on end reliably, TM is a terrible choice. It won&#x27;t do that. If you can deal with the regular FUBAR&#x27;d backup and redoing it from scratch (so you have about a 24 hour period with either no backups or two separate backups) it&#x27;s not a bad system. Sure is better than whatever Windows 7 offers which will never remove old data and will inevitably lead to full disks.