Hello,
please try "127.0.0.1" IP address. If it still doesn't work, probably there is a configuration problem and your server doesn't allow local network connections via port 80 (http) - as a result sitemap generator is not able to crawl the site. This is usually related to firewall installed at the host - could you please contact your hosting support regarding this?
Also, in some cases this can be fixed with DNS Doctoring operation on the server.