Yesterday Time Machine on my MacBook started to fail with the message:

“The problem may be temporary. Try again later to back up. If the problem persists, use Disk Utility to repair your backup disk”

It kept erroring after each hourly backup attempt. So I tried the obvious and unmounted the external HDD, turned off/on, remounted, ran backup again, no dice.

I ran Disk Utility to repair the disk, no dice.

I then found this forum post , which led me to the absolutely fantastic Pondini site (the link on the forum post is old, you need to go here) and smacked my head because I’m an idiot, I already have the Time Machine Buddy widget on my Desktop, just been so long I had forgotten.

That showed me:

“Starting standard backup
Backing up to: /Volumes/2TB/Backups.backupdb
Waiting for index to be ready (101)
2.52 GB required (including padding), 1.18 TB available
Indexing a file failed. Returned 1 for: /Library/Spotlight, /Volumes/2TB/Backups.backupdb/Apple’s MacBook Pro (2)/2013-09-03-071009.inProgress/C981E713-FC42-4A7D-BDD5-C83709DF0D5B/Macintosh HD/Library/Spotlight
Aborting backup”

Which shows that Time Machine has been choking on a Spotlight search file, which in turn led me to notice that my Spotlight seemed to be taking forever to complete an index (you can tell Spotlight is indexing, there’ll be a tiny black dot in the circle of the Spotlight magnifying glass top right of your screen).

In fact, the hours remaining at one point said “About 11 MONTHS” remaining. Not encouraging. I know there’s a way to force Spotlight to reindex your Mac:

• Open System Preferences
• Click Spotlight icon
• Click the Privacy button
• Add your HDD to the list “Prevent Spotlight from searching these locations”
• Close System Preferences
• Re-open, click Spotlight icon, click Privacy button, remove your HDD from the list, close System Preferences

This should kick off a fresh index, it’s much easier than one method I figured out a while ago where you manually delete the Spotlight index file (at one stage my Spotlight decided it didn’t want to index my local hard drive, just my external drives).

So far so good. Time Machine successfully completed its last backup. Spotlight has been sporadically re-indexing, but appears to be returning correct search results when I try a few tests.