I've tried to get the APXS reading on a rock in the Victoria Crater rover mission several times and in several ways... it always says no target in range. I got the both ends of the rover right into the designated area and right up to the rock even... and still no target in range.

First time I did the mission, the APXS was on the front of the rover and the camera on the back, so I had to drive the thing backwards to see where I was going. On the second time, I switched the positions of the camera and the APXS, so I could drive forward, but the APXS still didn't work.