It's possible that the domain name associated with the additional site is not yet correctly pointed to the server where your site is installed (via IP address or, if your site is hosted by Blackbaud, via CNAME record). If this is the case, when you change the DNS settings for your additional site's domain name to point to the installed location, the new site should be fully editable.

Additionally, you may have a redirect in place for the new domain pointing to the original domain of the main site. If this is the case, remove the redirect and, provided the new domain's DNS settings point to the installed location of the NetCommunity site, the new site should be fully editable.