what server OS are You running? OSX Mavericks Server or the normal version? If it's the server OS, this could be a reason..
Just the regular client version.
We are well aware that FileMaker Server 13 Admin Console highjacks port 80, which renders many of the OS X Server services inoperable. It's really sad.... two server configurations are now required for OS X users that need a web server to host a web site and want to have access to the OS X Server app for easier configuration and use. We know the 2 server configuration provides better performance. However, sometimes better performance isn't required and smaller companies don't want to shell out $15K for 2 servers when 1 will be fine.