$GUI_DISABLE is not available so I have @SW_DISABLE which may be my problem, but from what I saw in the extended style table I thought this was the correct choice. I also added several includes as I'm not sure which includes these variables yet. This snippet shows what I'm talking about - button1 is invisble and button2 is not disabled.
#Include <Constants.au3>
#include <GUIConstantsEx.au3>
#include <ButtonConstants.au3>
#include <WindowsConstants.au3>
Dim $b1, $b2, $bx, $hGUI
$hGUI = GUICreate("Test",200,200)
$b1 = GUICtrlCreateButton("Button1",20,25,50,15,-1,@SW_DISABLE)
$b2 = GUICtrlCreateButton("Button2",20,50)
$bx = GUICtrlCreateButton(" Exit ",20,100)
GUISetState()
GUICtrlSetState($b2,@SW_DISABLE)
While 1
$msg = GUIGetMsg()
Select
case $msg = ""
case $msg = $b1
MsgBox(0,"","button 1")
case $msg = $b2
MsgBox(0,"","button 2")
case $msg = $bx
Exit
EndSelect
WEnd