That mounting screw isn't a ground. The screw holds the plastic socket to the underside of the dash. You've either got a bad bulb or the socket connectors are corroded. If the bulb on the other side works, then I wouldn't suspect a ground problem. The other thing it could be is the wiring on that side may have a split.
I would take that screw out and see if you can drop the socket to check it out. To really see what's going on, you may have to pull the glove box and the passenger side A/C duct. Not too hard to do.
Do you have the power trunk release option too?
