Yesterday, my MacBook Pro gave me the message that for reliability reasons, Time Machine should make a new backup. In short, it means that all the backups I had before had become worthless and that I should start all over. I thought that was quite worrying for a backup tool. I found this thread that spans 25 pages over 2 years on Apple's support site. No solution yet: https://discussions.apple.com/thread/3684176 It turns out the error also appears on Apple's own Time Capsule. I didn't find a thread on this topic on this forum, that's why I'm posting one now. If anybody has a workaround, that would be helpful. I'd rather not use a USB disk. My backup target is a home-built NAS that presents itself as a Time Capsule to my Mac.