I searched the Apple "Community" Support forums and found several related questions, with lots of "I have the same issue" tags, but with no helpful answer:
So I did figure this out on my own.
If you get this error when trying to connect from your Mac to the Personal Hotspot of your iPhone, try the following for a fix:
There is a file called "com.apple.airport.preferences.plist" in the folder "/Library/Preferences/SystemConfiguration".
If you cannot locate it directly, use a tool to find it, e.g. with my program Find Any File (no need to pay for it if you only use it once - just download it).
Then make a back-up of the file, in case you get it wrong below! For instance, copy the file to your Desktop.
Then you have two options:
- Delete this file. But that will also reset all your network interfaces, e.g. if you had set up a LAN connection with a fixed IP address or made other configurations in the System Preferences' Network panel. And after deleting it, you need to restart the Mac so that it sets up the network interfaces again. Then try to connect to the phone again.
- If you're more adept, edit the file, e.g. with the app PrefEdit or BBEdit, then find all entries that mention "phone", and remove those. After saving the changes, you should be able to reconnect to the phone without even requiring a restart.
If something went wrong, copy the backed-up file back into the folder (you'll have to enter your admin password).