Not Valid Method 
Using:
target="_blank"
in HTML to make a link open in a new window will not validate.
Valid Method 
Here’s how to fix it..
1. Use:
rel="external"
instead of:
target="_blank"
in your HTML code.
2. Copy and paste:
$(document).ready(function() {
$("a[href!=''][rel*='external']").attr('target','_blank');
});
into a new document and save as:
external.js
3. Upload ‘external.js’ to you domain.
4. As this code uses jquery you will need to tell your site how to understand jquery.
5. This can be done by downloading the jquery file
here and uploading it to your site or simply calling it from somewhere it is hosted.
6. Find your head tags:
<head></head>
in your HTML code and add:
<script type='text/javascript' src='http://www.yourdomain.com/jquery.js'></script>
<script type="text/javascript" src="http://www.yourdomain.com/external.js"></script>
BEFORE
</head>
e.g:
<head>
<script type='text/javascript' src='http://www.yourdomain.com/jquery.js'></script>
<script type="text/javascript" src="http://www.yourdomain.com/external.js"></script>
</head>
7. Make sure you call ‘jquery.js’ before files that are set to use jquery.
Thank to
Matt for helping me with this.
