Element.getAttributeNode(name) is throwing DOM Exception while accoring to Java Docs & also according to the source file, it is not supposed to throw any such Exception. This method returns an attribute node by name & it's supposed to return null if the specified attribute is not there.
Even Element.removeAttribute() is throwing the same exception as it might be giving call to getAttributeNode() internally to get the requested attribute to be removed.
Run the attached file & if you find "sun.plugin.dom.exception.NotSupportedException: Element.getAttributeNode() is not supported
" displayed on the loaded applet than the bug is reproduced