Can't get domain mapping to work

Hello, for some reason I can't get my domain to hook up with my site. I'd like to map to When try to link it up, a red warning comes up that says "Domain name is unavailable to access". I must have the DNS set up wrong, but I don't understand what I did wrong. I have the A record pointing to the site's IP address.

I attached a screenshot of the error dialog box to this message.