I am experiencing the same problem. (pop up window stating: your network settings have chagned... ) I have to force quit system preferences to close it. Have you any luck correcting this?

Click on the apple icon in the upper left hand corner of the menu bar. Select "Force Quit" A window opens.. select system preferences, then click on "force Quit" another box opens asking if you really want to do this, click on force quit and there you go. you made the system preferences box close. this doesn't fix the problem we are experiencing. When I open sys pref again and select Network the drop down box comes back and the only way to get rid of the whole thing is to do the force quit operation again. I went to the genius bar and the guy told me to back up my stuff and come back and ask to have my hard drive erased and reinstall the OS and this will probably correct the problem.then you have to rebuild all your data. Seems like a lot of trouble. Before I do this I'll keep researching other means.

I found some alternate info elsewhere. The issue is with a security patch Apple released. They changed the way PPP and PPPoE passwords are maintained on your system. To fix it you first need to make that lame "Your network settings have been changed by another application" dialog stop popping up. To do this open "System Preferences" and go to "Security". Tick off "Require password to unlock each secure system preference". Now click "show all" at the top. I had to quit "System Preferences" to make the change take effect. Open "System Preferences" again and choose "Network". You will probably get the annoying pop up once, but this time when you click "OK" it won't loop. Notice that the padlock in the bottom left corner is now locked. Click it to unlock. Enter your password (assuming you are the administrator on the Mac). Now click back on the show all button. The Mac will think you made a change and ask if you want to " Apply configuration changes" click "Apply". Once it saves the changes your problem should be fixed. You can go back to the "Security" pane and untick the option you enabled earlier.

There is one catch to this fix that had me stumped for a good while. If you have ever used an external modem on your system there could be PPP settings that you can't get to without having the modem attached. What a pain! I could see "External Modem" in the port configurations, but it was grayed out and I couldn't make any changes. The only way to edit the PPP password was to find a modem and plug it in. "External Modem" became an available option and I could now edit the settings. Such a stupid problem! Hope that nugget helps anyone stuck in a similar situation.

Thank you for posting this fix! I have tried several things without success, and this is the only thing that worked; plus, it only took seconds to do, and worked instantly. No more looping. Clear instructions are very appreciated.

Brilliant! James, thank you so much for this simple fix. I've just locked the padlock in the security pane, and this was sufficient to kill the bug! Genius, you are.