Originally Posted by bbrown302
I have read that the issue might be an open neutral and not a hot / ground reversal. I would think that a hot / ground reversal would trip breakers. But, I don't understand how an open neutral would occur when you flip a light switch on.
My guess is that there's a poor connection on the neutral somewhere in that circuit. The poor connection passes enough current so that, with nothing else on the circuit switched on, it reads normal on the plug-in outlet tester. However, when you switch on a light, the neutral can't pass enough current for the light to light. The neutral goes to line potential. That makes the hot-to-neutral light on your tester go out, and the neutral-ground light comes on.
Start pulling out the switches and receptacles on that circuit and checking the neutral connections.