When you encounter the error “there was an error joining the AirPort” on your Mac, you can try one of the following to re-establish your connection:
1. Restart your machine by clicking the Apple icon in the top left coner of your screen and choosing Restart from the drop-down menu.
2. Turn the AirPort off and back on again. You can do so by clicking the AirPort or Wireless icon in the upper right hand corner and choose “Turn WiFi Off” or “Turn AirPort Off” depending on the version of OS X you’re running. After doing so, repeat the process to turn it back on.
3. You can choose “Other” from the AirPort menu and enter the network name and password manually.
4. Another optoin is to go into your keychain (/Applications/Utilities/Keychain Access). For each of the keychains (the top-left box), select it and then choose Keychain Access -> Keychain First Aid and do a repair.
5. If that doesn’t fix it, look in both your “login” keychain and the “system” keychain and delete all the keys whose kind is “AirPort Network Password”.
Depending on the exact issue you’re facing, any one of the steps may fix the problem.
