Wrong height

[defsdoor]

var flashHeight = $('.flash_message').css("height");

Should be

var flashHeight = $('.flash_message').innerHeight();

I've also changed the bulk of the js to -

  var fm = $('.flash_message');
  if ( fm.length>0 ) {
    // Grab height of Flash Message
    fm.each( function() {
      var flashHeight = $(this).innerHeight();

      // Calculate closed position of flash message
      // Negate height, parse to integer, add CSS shadow height
      var closePos = "-" + (parseInt(flashHeight) + boxShadowOffset) + "px";

      // On Document load, slide down flashes then slide up after delay of 3 seconds
      $(this).animate({ marginTop: 0 }).delay(delayTime).animate({ marginTop: closePos });

      // Dissmiss Flash Messages
      $('#flash_close').click(function(){
        $(this).stop(); //Stop Animation
        $(this).animate({ marginTop: closePos }); // Slide up
      });
    } );
  }