Solution for Time Machine error “Unable to complete backup. An error occurred while copying files to the backup volume”

My SO has a Mac, and she was using Time Machine to back it up.  As someone who cut his teeth with Amanda backups back in the day, Time Machine is a beautiful, intuitive backup solution.  Really, it is.

However, a while ago the backups stopped working.  She saw this error message: “Unable to complete backup. An error occurred while copying files to the backup volume”.

I googled around for it and saw this KB article from Apple, which wasn’t too helpful, as the only troubleshooting suggestion was a reboot (hmmm, sounds a bit like Windows).  I tried doing that multiple times, and still saw the error message.

So, we tried a different hard drive.  That still didn’t seem to work–same error message.

Finally, I did some more googling and ran across this forum post (yes Jeff Atwood, forums are indeed the dark matter of the web), which gave me additional troubleshooting tips.

Basically, if you are seeing this error on time machine:

1. connect your time machine disk drive to your Mac
2. turn off time machine by opening the time machine prefs and select ‘none’ for the backup disk
3. open up your console
4. click on ‘system.log’
5. click ‘clear display’
6. turn on time machine by opening the time machine prefs and selecting your disk drive
7. watch the system log for errors that look likeMar 9 12:14:14 computer-name /System/Library/CoreServices/backupd[905]: Error: (-36) SrcErr:YES Copying /path/to/file/file.name to (null)
8. remove those files
9. restart time machine by repeating steps 2 and 6.

I am not sure how to fix the issue if you can’t remove those files.  The files that were causing issues for our Mac were imap mailabox files from Thunderbird, so I just uninstalled Thunderbird and removed the mailbox files.