When my WoW toon first shows up in Azeroth I get an error box with the following message:

Interface\Addons\Cartographer\Cartographer:lua:1:attempt to index global 'Rock' (a nil value)

and an "ok" button. When I clidk the button the message goes away. Is there anyway to get rid of this message and correct the error?

TIA for any help

Wait for an update of the addon to fix the problem.
http://files.wowace.com/Cartographer/Cartographer.zip

Lots of us had that. I had 3 other bugs as well.
But the new update took care of them all!