[Phanx]

Well, that error is certainly interesting, because it names line 585, which is a blank line in the file you posted...

Anyway, I don't see anything immediately obvious, and don't have time right now to comb through everything to figure out what's going wrong, but I'd suggest using a more robust recycling system for your textures.

local textures = {} -- textures in use

local GetTexture, FreeTexture
do
	local pool = {}
	function GetTexture(parent)
		local texture = next(pool)
		if texture then
			pool[texture] = nil
			texture:SetParent(texture)
			return texture
		else
			return parent:CreateTexture()
		end
	end
	function FreeTexture(texture)
		texture:ClearAllPoints()
		texture:SetParent(nil) -- might need to use UIParent instead of nil here
		texture:SetTexture(nil)
		pool[texture] = true
	end
end

Mixing used and unused textures in the same table seems like a recipe for trouble.

Also, when you clear the texture, don't forget to nil out the reference to it, eg:

bar.segments[firstVisible].tick = ns:freeTempTexture(bar.segments[firstVisible].tick)

I didn't look very far, but this may be related to your problem.