I'm on MacOS High Sierra Version 10.13.2 and use Time Machine to back up to an external drive through an AirPort Extreme.
I've had this setup for years (~5, I think) and backups worked fine until earlier this year. The .sparsebundle file has a Date Modified of Apr 30, 2017... I don't know whether it broke after an OS update, or anything like that. When attempting a backup, I first get the following message:
Time Machine completed a verification of your backups on “Chris' AirPort Extreme”. To improve reliability, Time Machine must create a new backup for you.
and I click "Start New Backup". Shortly after, I get the following error:
Time Machine couldn’t complete the backup to “Chris' AirPort Extreme”. Time Machine could not delete the backup disk image “/Volumes/FreeAgent 3TB GoFlex Drive 0-3/Chris’s MacBook Pro.sparsebundle”.
I've bolded "0-3" because, the thing is, the name of my drive as connected through the airport is "FreeAgent 3TB GoFlex Drive 0" -- I have no idea why the plist file has "-3" in the path.
I had a go of editing /Library/Preferences/com.apple.TimeMachine.plist to change the "0-3" to just "0" (I did this by turning off automatic backups in Time Machine preferences, using plutil to convert the plist to xml1, edited in TextEdit, then converted back to binary1); however, when I turn backups back on and tell Time Machine to Back Up Now, it just overwrites the plist to include the "0-3" again.
Same goes for when I delete this plist, entirely -- a new plist is created with "0-3". Any ideas?
UPDATE: Before posting this, I tried a tip I found which advised to repeatedly delete the plist then restart until the plist stays deleted — this never happened (a com.apple.TimeMachine.plist file has always been present after restarting) but the “0-3” has changed to “0-2”.