According to the network sharing troubleshooting guide:
That error only presents itself when you have two installations of filemaker (server & pro, but possibly also other combinations), running on the same machine.
Did you ever install a trial of filemaker server in the past? Do you have an earlier version of filemaker running (e.g. FM12) ?
I would first reboot the machine, then take a look at the running services/processes (under task manager), and see if any filemaker things are running.
port 5003 has nothing to do with that error, nor does the ipad.
The above link from Mike is definitely the best place to start. It's usually caused because another FileMaker Pro version is trying to host, or FileMaker Server is installed. However, it is also flagged in some cases when another program is using port 5003. The iPad is irrelevant, but if you have other server software or anything at all hosting or communicating, even Security / Anti-virus may flag this error. Just things to check on. I would see if 5003 is talking and if it is, what's using it. If it's not talking, most likely security/anti-virus.
you can check for what programs are "listening" on port 5003 by running the cmd utility (windows) and using the netstat command.
Something like netstat -b -a
alternatively there are simple GUI programs like: http://www.nirsoft.net/utils/cports.html
that will allow you to view "listener" ports.