Issue with Object Oriented Programming in Lua

I have created a render Lua file, and created multiple objects, I have copied a small snippet of the file. This is the Object (class) that I am having issues with. When the newBox function is created the this:show() is causing the error in the Box:show() when the function registerBox() is called. An attempt to call nil

However I have played around with the syntax a bit (stretching one line into multiple lines to figure what part of the line is causing the error) I know for a fact that the function is not causing the attempt to call nil, it is the this.x or any of the this.<var> Am I not passing the variables correctly? Remember this is only a snippet, all of the functions called are left out so I don't have to post 750 lines of code.

Also I have commented on a few things to help you understand what I mean a little more, and so you don't need to read all of the code line by line as much.

-- Box Class

function newBox(x,y,z,w,h,t,b,c)
  local this = setmetatable({}, Box)
  this.x = x
  this.y = y
  this.z = z
  this.w = w
  this.h = h
  this.t = t
  this.b = b
  this.c = c
  this:show()
  this.v = true

  return this
end

This is called when a new object is created for example local obj = newBox( ... )

function Box:render()
  rasterBox(this.x,this.y,this.w,this.h)
  renderBox(this.x,this.y,this.w,this.h)  
end

This renders the box, don't worry this is all working fine...

function Box:move(x,y,z)
  this:hide()
  this.x = x
  this.y = y
  if z then
    this.z = z
  end
  this:show()
end

function Box:resize(w,h)
  this:hide()
  this.w = w
  this.h = h
  this:show()
end

function Box:pattern(t,b,c)
  this:hide()
  this.t = t
  this.b = b
  this.c = c
  this:show()
end

The code above should not have any issues, SHOULD...

function Box:show()
  registerBox(this.x,this.y,this.z,this.w,this.h,this.t,this.b,this.c) -- CALL NIL ERROR
  this.v = true
  this:render()
end

The function above is called when the object is created > this:show() it is NOT the RegisterBox function it is the actual this.[var] parameters. Below is the rest of the code. not sure if the code below is causing any issues though.

function Box:hide()
  unregisterBox(this.x,this.y,this.z,this.w,this.h)
  this.v = false
  this:render()
end

function Box:getPosition()
  return this.x,this.y,this.z
end

function Box:getPattern()
  return this.t,this.b,this.c
end

function Box:getSize()
  return this.w,this.h
end

function Box:destroy()
  this:hide()
  this = nil
end