Red exclamation mark when trying to update Nexus 7. Every time I go to update my Google Nexus 7 to Android Jelly Bean 4.2, it fails and shows the Android logo on it's side with red exclamation mark (!) on. 

Why won't it let me update to Jelly Bean 4.2?

Has anyone else had this issue before?
I had this problem because I manually (via titanium backup) uninstalled one of the system apps: the korean keyboard (which, for me, is rather pointless). Somehow that caused the upgrading process to fail, maybe because my system was not "intact". After I restored the app it worked flawlessly. Did you make any modifications like that? If so, try reverting them.