I wrestled with this for a while before noticing the view source showed the url to the skin was encoded.
skin : "http%3A%2F%2Fwww.blahBlahBlah.com%2Fdev%2Fjw%2Fwp%2Fwp-content%2Fuploads%2FjwPlayerSwfForWordTube%2Fstijl.swf",
skin : "http://www.blahBlahBlah.com/dev/jw/wp/wp-content/uploads/jwPlayerSwfForWordTube/stijl.swf",
I found on line 611 in the /plugins/wordtube/lib/wordtube.class.php file the following. Making the change solved the issue.
$this->swfobject->add_flashvars( 'skin', rawurlencode($this->options['skinurl']));
remove the 'rawurlencode' from this so it looks like this
$this->swfobject->add_flashvars( 'skin', ($this->options['skinurl']));