To everybody that is getting PTR 4.3 errors. Apart from the division by zero errors related to unit power, it is more likely than not due to a bug in Blizzard's SecureGroupHeaders.lua file, line 810.
They have added this nifty line on the PTR 4.3 versions of their code, which is not present in the live versions:
lua Code:
local deadIndex = #display + 1;
The problem with that, is that "display" is a number value. Not a table. Which means it's the Blizzard code that bugs out, and no addon in existence can fix that. Get rid of the "#" and it should work fine, as far as I can see.
I have reported the issue in the EU PTR forums, as didn't know where else to turn to. It might already have been fixed, in the 1.1GB patch I'm currently downloading, but I still reported the issue. Better safe than sorry. And I hope this might help some other addon developers like me that is banging their head against the wall of line 810, not understanding why they can't fix their addons!
http://eu.battle.net/wow/en/forum/topic/2793451767#1