Breaker trips when turning switch on with no load (No GFCI)
If you didn't test the wiring periodically as you installed it, it is now for you to do.  

I would sever off lamps 4-7 at the lamp 3 junction, relight, see if the problem clears.  Then divide the remaining area-of-uncertainty in half and repeat, in half again repeat.  Now you are down to 1 light, it is that light or the one before.   

If it helps, get some 3/4" plywood and lay it across the joists so you have a roadway and don't put your foot through the ceiling.