outside motion light sometimes not working

i have a outside garage motion light 100watt bulb...it keeps intermittently not working.. it is brand new. there was a metal cross bracket alreay there, but i needed to also us the cross bracket from the new light. so there are 2 metal cross brackets mounted. i was wondering if that could be causing the issues. or i think maybe i did not have the ground wires hooked to the green screw correctally. after i did that (both ground wires clapped to green screw) it seems to be working correctally, but it have only been one or two days. LOL [IMG]