It looks like this is a common problem so I would guess that BCS has seen it before and maybe they would share some info as to the cause. It is likely due to some weak point in the wiring, like what Karl mentioned, or a breaker or fuse that hides somewhere. All of the lights are in parallel wiring wise and you could pull one of them, gain exposure to the wire, and test whether you have lost the ground or the + side with a volt/ohmmeter. If it is the ground then you possibly might be able to pick up a ground somewhere and tie it in again to any one of the lights. If the plus is missing that might point to an unknown fuse or breaker or junction point. If the switch passes the plus then the open is between the switch and the first light in the chain, wherever that junction point is.
Good luck with this...
Later Ed