[Clamsoda]

Nothing related to the arena frames is available until Blizzard_ArenaUI is loaded. I can confirm that it does not become loaded upon normal log-in circumstances.

You need to execute the relevant code once Blizzard_ArenaUI has been loaded; listening to ADDON_LOADED can provide you with that information.

Phanx has much more time invested into your code, I'd rather let her deal with refactoring it to allow for the circumstance.

Edit: The reasoning behind the error is that your for limit, MAX_ARENA_ENEMIES, is a nil value.