Thank's to ericand for the great discussion about fixing the jammed lens which generates the system error 0042.
I had found my g500 in an open position w/ a dead battery after several weeks in my briefcase. I charged the battery and rec'd both a system error 0042 as well as an 004E.
I took off the front case per ericand's great instructions and was able to move the partially retracted lens outward, but not into its full recessed position -- by spinning the cog at the base of the front. With the battery back in, the lens moves out to full position, then retracts to the jammed point. When there, the spring response to the cog is present, and I can't move it down any further. It appears the gearing position of the lens has slipped as it "thinks" mid way is totally recessed.
I've tried removing the circuit board -- to get a better look at the lens gearing -- but am limited by a ribbon connector on the right edge of the board (looking at the lens) which seems solidly connected.
Any suggestions anyone?