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I had to go a couple steps further as my error turned into a '500 server error' after I deleted the NetworkInterfaces.plist and rebooted.

Try this at your own peril as ymmv. Some of this may not be necessary as this was an excercise in trail and error.

Delete the following from /Library/Preferences/SystemConfiguration

NetworkInterfaces.plist

com.apple.network.identification.plist

com.apple.airport.preferences.plist

This seems to have something to do with the AirPort config - so that all needs to be reset. Once these are deleted - reboot. The NetworkInterfaces plist will rebuild.

After boot - open network configuration and delete the AirPort interface from the Automatic profile. Then immediately add it back. (not sure why I had to do this - but it didn't work otherwise). Now reboot again.

After reboot - make sure the AirPort is turned on - you may need to give it some time to sort things out and find your networks. At this point things may be fixed.

Please don't do this unless you are comfortable jacking around with stuff that may make things worse.

This worked for me too:

1) Delete the file Macintosh HD/Library/Preferences/SystemConfiguration/NetworkInterfaces.plist

2) Reboot

3) Sign in to the app store.

voila

p.s If you don't know how to do this, then I would caution you on messing around with system files - but if you are aware of the possible consequences (rare if you follow the instructions)

1) click on the finder

2) click on 'Go' (top menu) -> 'Go to Folder...'

3) copy and paste this into the field (minus the quotations) " /Library/Preferences/SystemConfiguration "

4) find and trash NetworkInterfaces.plist

5) reboot

HERE'S THE FIX JUST GIVEN FROM APPLE SUPPORT THAT WORKED FOR ME.

Turn off your Firewall

Delete the Network Interfaces.plist

Create new Network Location

Reset the SMCPRAM (prameters) Restart

Log Back into Apple App Store

Turn on your Firewall

Works!

I did this. It worked.

Great to hear it worked for you !

Thanks, Robbie.

After two days of getting nothing from Apple Support, your fix worked a charm. Does make you wonder if the people on staff at Apple to help with support functions ever read these forums, doesn't it?

Again, thanks for posting this fix.

No problem - glad I could be of help. I know someone who workes at the Apple Support center... and let's just say the training is.... not the greatest.

Anyway rock on.

I had this same problem on my computer and my wife's computer. Your fix worked on mine, but it doesn't work on my wife's. Any ideas?

When I did it on mine, it asked me for my router key, but for my wife's it hasn't. It doesn't seem to "forget" the network info like it did for mine.

Hm.. That means the file isn't getting deleted. When you trash it, do you empty your recycling bin? That shouldn't really have an effect... as long as the network file isn't in it's proper dir the computer should be forced for make a new one.

In some of the othe posts they recommend deleting extra files, try that.

Good luck, report back

I deleted the other 2 files and all the other steps, but it still didn't work. It still doesn't seem that my wife's network preferences are deleted because it still doesn't ask for the network key when I start it up like it did for my own computer.

I'm still at a loss. I really don't want to take it into the Genius Bar, but I may have to.

The sad, but funny thing is that when I called support, they gave me the choice of coming here to find the answer, go to a Genius Bar, or they would help me for $50. Really? $50 so they can help my buy mroe stuff from them? C'mon.

This worked perfect! Thanks!!!

Deleting the networinterfaces.plist file worked a treat.

Thanks for the help everyone!!

What worked for me was deleting both NetworkInterfaces.plist and preferences.plist then rebooting.

I don't know what is stored in preferences.plist (I'm a new Mac user) and I would not recommend you delete this file unless you know what you are doing - but I 'inherited' this laptop from my teenage son who has recently got a new one, so I really needed a clean setup anyway.

However I did notice when I first set up this machine for myself that it wasn't picking up DNS settings correctly for either ethernet or wifi connections and I manually had to enter a DNS. I don't know if that was related or not, but it wouldn't hurt to check the various TCP/IP (such as DNS and gateway ) before deleting various files if you are experiencing this issue.

In addition to deleting the plist files, try deleting the services in the list in System Preferences/Network, restart and then add the services back. To delete a service, highlight the service and click the [ - ] symbol below.

Free phone support is only the first 90 days after buying a new Mac. Then it is USD$50 a whack. Unless you have purchased an Apple Care plan and then you have phone support for the 3 years of the warranty.

I am not sure why they would send you to the Apple Genius, the genius is there for hardware issues, not software issues. If you come in with software issues they will offer to erase and reinstall Mac OS X without making a backup or send you away.

Hi,

I have the same problem. Either deleting the 2 files or reseting the SMC is useless. Btw, my built-in ethernet card seems to be out of order (no hardware detection in the system hardware list). I think both problems are related, and that Appsotre checks the integrity of my computer before allowing me to connect :/