[wagonis]

So I've been battling with my 4.2 update, every time I tried to run the update I kept getting the annoying dead Android with the red triangle notice. I've tried to run temp unroot, disable Super User and was about to flash a stock ROM but was afraid to lose everything and start over. I read in several threads that the update will run a checksum to validate the image has not been altered so I started to trace back everything I did to my N7 since i got it and here is what I had to do in MY case, as yours might differ:

1.) A couple of months ago I edited my /system/build.prop in order to get the tablet UI instead of the phablet UI. If you've done the same and made a backup copy of this file before editing it, just place the backup copy back in the /system dir and move the edited in to a dir elsewhere on your storage. If you choose to just edit the file back to it's normal text, make sure you also change the permissions back to rw-/-/-
2.) Another change I made was to the /system/etc/media_profiles.xml in order to unlock the 720p video recording. Follow the same steps above to restore that file to it's original state.
3.) Last major change I made to any system files was to enable flash support via the Android browser. Part of that was to rename the following files in /system/app:
- BrowserProviderProxy.apk to BrowserProviderProxy.apk1
- BrowserProviderProxy.odex to BrowserProviderProxy.odex1
Just rename them back to their original names
4.) Made sure I was still on temp unroot and Super User disabled
5.) Went in to Settings >> Apps >> All and forced stopped the Google Services Framework, then cleared all data

Once I completed all the above, I restarted my tablet and it prompted me to update my firmware and this time it went through successfully and I am now on 4.2.

Hope this helps anyone else or at least points them in the right direction.

[oldmancolin]

This worked for me, thanks! I did lose root access in the process but re-doing that was a lot easier than having the device wiped.