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Fixing “Your Mac was unable to communicate with your Apple Watch”

After reseting an iCloud password, every Apple device that uses the iCloud account will need to authenticate again. For an Apple-centric user, that would be an iPhone, iPad, Apple Watch, Macbook and may be a few other devices. All seemed to go well except the Apple Watch no longer unlocked the Macs. Even unpairing and re-pairing didn’t fix the issue with various errors including “Your Mac was unable to communicate with your Apple Watch” after re-pairing the watch to the phone. But thanks to this tip from user stoska992 on Apple Communities, the problem is solved.┬áSteps:

  1. Open “Keychain Access”
  2. In “View”, enable “Show Invisible Items”
  3. Search for “Auto Unlock”
  4. You should see a whole bunch of application passwords for “Auto Unlock: XXXX’s …”
  5. Select all records and delete (this will reset/disable auto unlock on other Macs if you use multiple Macs)
  6. Whilst still in “Keychain Access”, search for “AutoUnlock” (no space)
  7. There should be 4 entries for “tlk” “tlk-nonsync” “classA” “classC”
  8. Select 4 records and delete (don’t worry if they re-appear, the system repairs this automatically)
  9. Open “Finder” and navigate to “~/Library/Sharing/AutoUnlock”
  10. There should be two files “ltk.plist” and “pairing-records.plist”
  11. Delete both files
  12. Open “System Preferences” and try enabling auto unlock. You may need to enable it twice, the first attempt will fail. [And you may need to restart your Mac as well before enabling Auto Unlock.]