As i have checked my site with webpage

Hello,

As i have checked my site with webpage http://www.statscrop.com/, my site have some issues about SEO. Please take a look their suggestion about optimize my site here: http://www.statscrop.com/www/hivietnam.net (right size bar, choose How to optimize hivietnam.net)

First of all, i would like to need your help about this issue. Please view this screenshot: http://imageshack.com/a/img197/6088/p8e9.jpg

I have the welcome page name hivietnam.net for customer choose to access two different languages page. In this page, i'm using "non-www to www" code in .htaccess for redirect "hivietnam.net to http://www.hivietnam.net".

.htaccess code below:
# Redirect non-www urls to www
RewriteEngine on
RewriteCond %{HTTP_HOST} !^www.hivietnam.net
RewriteRule (.*) http://www.hivietnam.net/$1 [R=301,L]

I don't know why search engine still think my site have duplicate content (because of hivietnam.net and http://www.hivietnam.net are showing the same page), so this is will decrease my page rank.

Please help me check.

Thank you,
Tuan.

p/s: i've turned on Suppost access in my page, in case of you need to access to take a look.