Your network settings have been changed by another application

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ka jowct wrote:
This is supposedly the fix...

That's not a fix. It's a workaround.

As soon as you go to change a setting the symptom will return unless you delete these files from the SystemConfiguration folder and restart:

com.apple.airport.preferences.plist
NetworkInterfaces.plist
preferences.plist
com.apple.nat.plist

Note that you'll have to redo your network pref's afterwards.

ka jowct wrote:
BTW getting rid of that folder did NOT work for me...

So far as I can recall (and I admit it's been a long time so I may not recall correctly), trashing those files has worked every time that I've encountered the problem.