I can't speak exactly for the AT&T variant, but running stump root on my Verizon G3 the other day it gave me the exact same issue...and seems to have worked out fine on my end ultimately. You can read my post on page 25 of that thread detailing my exact experience if you're curious!
XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Are you a developer?