1.12 to 2.1 : Navigator module not installed

[Pavlov]

So therefore the issue is.... you didn't properly restore before you attempted the next upgrade. Probably due to not clicking the correct boxes in phpmyadmin or something.

Yes.

[Jean le Chauve]

And if the installer was with no issues, the user would probably not have to restore the site...
As you can see, there was some people with this problem. Perhaps a BD check within the next versions...