TTT's AddColumn gives a nil value

In short, I am trying to create an mysql-based EXP system for TTT. Everything else is set and working, but I’m encountering an issue where it is not able to display any of the information as “AddColumn” apparently is a nil value. I have absolutely no idea how to wrap my head around what is causing this. If it matters, here is the part in question:

if tttexp.Enabled == true then
	ply:AddColumn("Rank", function(ply) return string.Comma(tttexprank) end)

Do not worry about anything else, as everything including ply is already defined. AddColumn is just what’s stopping me here. I cannot really provide anymore information than that since this is the only single part of the addon that has to do with the scoreboard at all. What step am I missing here?
If anyone is wondering the exact error:

Here’s a quick tut on how to use it: - remove .html for .lua

It includes a lot of text so, if you wanted to see the original topic, it is listed at the top!