Metal camera housing sparking on a metal building
Treat grounding seriously

This is a "canary in the coal mine".  And what its warning you to do is do a serious evaluation of the Grounding Electrode System for each of the buildings.  However I would advise only a cursory inspection - that the Grounding Electrodes are present and intact, and that the main panel has an intact neutral-ground bond - until you have evaluated and eliminated from suspicion the PoE camera. See if they have done something dumb like grounding one side of the PoE.  (If the injector grounds one side, and a load grounds the other, poof!) 

If the PoE injector and camera check out on the bench, then do an exhaustive search of the complex's Grounding Electrode System - ground rods on each building, netural-ground wired separately to each building with N-G bonds definitley absent in subpanels, etc. Start putting GFCI breakers/devices on circuits under suspicion. Etc. 

Grounds first, then circuits

Other than that, this sounds like the classic "I hooked up the circuit and it works, but when I hook up the grounds the circuit fails. What's wrong with my grounds?"   The grounds are fine. This is a perception problem: the circuit is actually dangerous, and ground is protecting it.  If you hook up ground first, then you see things as they actually are... because connecting live conductors  is the last thing you do, so the problem is obviously there.  

So ground that box.  Then hook up the camera!  The problem will "move" to where it actually is.