I think the solution is quite clear. Eagle needs to have the PCB trace go to the center of the pad. Even though the trace in the picture is touching the pad, it does not consider it connected. I would rip up what is there, start the trace from the pad, and then draw out to the GND plane. Make sure you use the Ratsnest command to make it re calculate the airwire if it is still there. Another option is to just manually run the wire, then if it is connected and you use the Ratsnest command, the airwire will go away. Now this is all for Eagle 5, but I would assume it's the same.