No overlay, just white div with 'False' when using modal dialog in ie6

No overlay, just white div with 'False' when using modal dialog in ie6

Hi Everyone.
 
I'm using the modal dialog within ie6 for an intranet application.  When the dialog opens, instead of getting the expected translucent overlay, I get a white div with 'False' in the top left corner.
 
I've attached a screenshot showing the problem.
 
The code I am using to generate the dialog is as follows:
  1. dialog = $("#dialog").dialog(
     {
      bgiframe: true,
      autoOpen: false,
      closeOnEscape: true,
      height: 500,
      width: 400,
      modal: true
     });







Many thanks,
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