OK, I tried all the solutions involving zapping the network from the previous Airport connection history, the Keychain & everything else I've seen here. Still no connection & the blasted self-assigned error message. I was so frustrated, I just threw up my hands and have been using my Ethernet cable to connect to the router, which I was pleasantly surprised to see worked... and ultimately led to the fix.
Tonight, after rubbing my sore butt from being chained to a seat at the dining room table for the last two weeks, I googled the problem AGAIN & was directed to this thread AGAIN.
FINALLY, I found my solution when I went to a YouTube link from a suggestion here, which didn't work; then I tried another video that popped up at the end of the first, which didn't work; but the third one that popped up at the end of the second was the charm:
http://www.youtube.com/watch?v=ulHud2DnVbI
I don't know why this didn't occur to me by myself. It needs an Ethernet connection to work.
Background: The problem was with my MBP connecting ONLY to my router at home. For 2-3 years, never had a problem. Suddenly, wham! I didn't download or update anything, just no joy on my home network <<insert salacious remarks here>>. Only MY MBP didn't work. All the other bizzillion Mac devices my kids use around the house, and my iPhone too, worked fine, so I knew it wasn't the router. Insult to injury: My wife's PC worked fine too. My MBP has continued to work at all the other places I normally get wifi away from home. MOST IMPORTANTLY, I could connect to the internet through the router using an Ethernet cable.
Again, I don't know why I couldn't try this one without the suggestion. You must have an Ethernet connection to the internet via your router working. Here we go:
1) Open Network preferences.
2) Click on Ethernet. Write down the "good" IP Address indicated.
3) Click on Airport. Select the troublesome network.
4) Click on Advanced.
5) Click on TCP/IP tab.
6) In first dialogue box, select: Using DHCP with manual address.
7) The IPv4 Address box will now allow you to type in the good IP address you found your Ethernet connection was using.
8) Click OK and you should be… OK!
My only concern is I WON'T be OK when I am away from home. In that case, I'll just follow the same path and go back just to Using DHCP. I'm hoping my MBP will be smart enough to know what to use when it encounters those familiar faces & places.
It's so amazing how crippled we are when our technology breaks down... and how euphoric we are when it gets fixed. I'm sure it says something terrible about our species.
I hope this might be the euphoria-inducing solution for some of you. Good luck!