tolua, Lua 4.x and enum problem

[pixellent@...]

I'm trying to expose some enums using tolua. My package file contains:

$#include "gui/hbGuiTypes.h"

$using namespace Habitat::Gui;

module Habitat
{
	module Gui
	{
		enum
		{
			HB_GUI_HORIZONTAL_LEFT,
			HB_GUI_HORIZONTAL_RIGHT,
			HB_GUI_HORIZONTAL_ABSOLUTE,
			HB_GUI_HORIZONTAL_CENTRE,
			HB_GUI_VERTICAL_TOP,
			HB_GUI_VERTICAL_BOTTOM,
			HB_GUI_VERTICAL_ABSOLUTE,
			HB_GUI_VERTICAL_CENTRE
		};

	}
}

tolua seems happy, and the tolua_hbGuiTypes_open() function executes no 
problem. I tried to access one of the enums in my Lua script:

	function StaticBitmap(t)
		local horiz = t.horizontal
		write(horiz)
		GuiManager:AddComponent(staticBitmap)
	end

then later:

	StaticBitmap
	{
		horizontal=HB_GUI_HORIZONTAL_LEFT
	}

But I'm getting:

error: bad argument #1 to `write' (string expected, got nil)
stack traceback:
   1:  function `write' [C]
   2:  function `StaticBitmap' at line 31 [file `scripts/testSDL/gui.lua']
   3:  main of file `scripts/testSDL/canvas.gui' at line 11
   4:  function `Exec' [C]
   5:  function `InitialiseGUI' at line 8 [file `scripts/testSDL/gui.lua']
   6:  function `OnStartup' at line 17 [file `scripts/testSDL/main.lua']
*** Error while running script file scripts/testSDL/canvas.gui

As far as I can see, I have done everything needed, yet I can't get this to 
work. I've looked through the code for the Doris project, and I can't seen 
anything drastically different. Am I missing something simple?

Many thanks
Mike

(PS - apologies for the long message.)