Hosting multiple domains

[Paul N. Pace]

I have a server that I set up to run several domains from and it has
worked great and without issue for about 6 months.

I have another server that I had set up and was only running one
domain from it and I just added a second domain. For some reason, this
second server does not want to serve two domains, and I can find no
substantial differences in the configuration files (nginx.conf and
sites-available files).

On both servers I put a symlink in the sites-enabled folder to the
corresponding sites-available file.

On the second, problematic server, when creating a symlink to the
second site and restarting nginx, testing the second domain only
brings up the first domain. Rebooting the server disables both domains
and the server appears unresponsive, except that I can SSH into it.
Then removing the symlink to the second domain and restarting nginx
returns the server to serving the one domain as it has been doing.

The first server is running nginx 1.5.0  and the second server is
running nginx 1.4.1.

What should I be looking at to resolve this issue?