Looks like your domain hasn't www DNS record.
Check DNS zone in your domain registrar web site and add "www" cname or a record for domain.
I've checked one DNS server of you domain:
[~]# nslookup www.retapy.com NS0.VPS380574-1.LCNSERVERS.COM
Server: NS0.VPS380574-1.LCNSERVERS.COM
Address: 178.18.126.170#53
** server can't find www.retapy.com.qa.plesk.ru: REFUSED