What does the error “htmlfile: invalid argument” mean? I'm getting this in excanvas.js

<html>
<head>
<title></title>
<script>
for(var i=0;i<32;i++) {
document.createStyleSheet();
}
</script>
</head>
<body>
</body>
</html>

var ss = null;
  var cssText = 'canvas{display:inline-block;overflow:hidden;' +
      // default size is 300x150 in Gecko and Opera
      'text-align:left;width:300px;height:150px}';
  try{
    ss = doc.createStyleSheet();
    ss.owningElement.id = 'ex_canvas_';
    ss.cssText = cssText;
  } catch(e) {
    ss = document.styleSheets[document.styleSheets.length - 1];
    ss.cssText += "rn" + cssText;
  }