HPS light problem

Tried to install a 50 watt HPS light. Would keep turning on and off after couple of minutes. Tried another fixture and same problem. Finally got it to work right by not having the ground wire connected.
Trying to figure out why this happened.
Also had checked no bare wires in box that could be touching.
Meter showed 119 volts between black and ground or black and white. Nothing between ground and white.

thanks

power

What about between the fixture's green wire and ground when the light is turned on?

Is this fixture being controlled by a motion sensor, or photocell?