Hi Laurena,

Arvixe uses Website Panel (WSP) for their hosting control panel, as does my hosting company, i7MEDIA.

Within WSP, to attach a domain to an existing website, you must create a domain alias, even if the domain is a sub-domain. So, you should delete the website that is named with your sub-domain (sample.interneteventregistration.com) and then delete the sub-domain (sample.interneteventregistration.com). Once you do this, you can create a domain alias and when you do this, you can select the option to point it to an existing website and select your interneteventregistration.com website. The domain alias pointing to your working mojoPortal site will setup the correct "headers" or "bindings" in the web server so that site will get requests for the sub-domain. mojoPortal will handle the rest.

If you need further helps with it, you should probably contact Arvixe Support because it's beyond mojoPortal's configuration to make it work.

HTH,
Joe D.