I tried adding the following in the subroutine, but it had no effect

sub Additional_Criteria
{
 #code her to test if check box is selected or not

   if ($chkoptions) {
      print "Enable\n";
      $lst_properties->configure(-state=>'normal');
   }
   else {
      print "Disable\n";
      #Code here to DISABLE ListBox
   }
}
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