网站重定向到www在使用SSH2（Secure Shell）的SFTP上不起作用

I am having a serious problem regarding website redirection to www if it is not appended in URL. My website works fine if I use www.domain-name.com but without www the site does not work and displays the following error in firefox -

I am using .htaccess and it has following code to redirect non-www to www -

RewriteEngine On
RewriteCond %{HTTP_HOST} ^domain-name.com$
RewriteRule ^(.*) http://www.domain-name.com/$1 [R=301]

I also tried following -

RewriteEngine On
RewriteCond %{HTTP_HOST} !^www\.
RewriteRule ^(.*)$ http://www.%{HTTP_HOST}/$1 [R=301,L]

But no luck.

One thing i want to mention is that this site has been setup on SFTP using SSH2 (Secure Shell). Is it would be the reason? Because before installing this protocol, the site was redirecting to wwww but not now. Then how can I rectify this issue? Thanks.