When running your Roll Call Server from a Mac, you may run into a conflict with Apache web server running automatically on your system. When typing in Localhost on your browser, it may plainly say "It Works!" in the browser. This is a clear indication that Apache is running and taking up your port 80 traffic. There are two possible solutions for this:
1. You may disable Apache entirely. This will prevent the Apache server from starting up automatically when your machine starts.
Open your "Terminal Window" (This can be found by going to your Spotlight search and typing Terminal )
sudo launchctl unload -w /System/Library/LaunchDaemons/org.apache.httpd.plist
This should be enough to get Apache out of the way by stopping it and preventing automatic start.
Alternate Solution if you need to keep Apache running for any reason...
2. Another option is to change the Roll Call Server's port that it listens on so that it won't conflict with Apache.
Note: if you go this route, you will need to reapply this port number change when upgrading/patching Roll Call as it gets reset to the default during upgrades/patches.