This occurs when the DNS server doesn't direct/redirect properly, if you have control over the DNS make sure that the w-w-w part of the CNAME and directs to the "at" of the A record.
If you do not have control over the DNS and you are on shared hosting, contact your hosting support to assist you with this.
Some hosting control panels have the ability to checkmark the redirection itself, which you need to disable it disabling the w-w-w in the cpanel.