Port 80 is the default. This can conflict with a web server (Apache is common)
You do not mention computer and operating system and version.
If you have multiple versions of Filemaker on the computer, they can conflict.
Port 591 is reserved for Filemaker.
Im using windows XP, I have two filemakers pro advanced installed in my computer, Filemaker pro advanced 10 and filemaker pro advanced 11, the .EXE file of my filemaker 11 was corrupted. for now Im using my filemaker pro 10 advanced.
Can I used port 591 when I changed my port no.?
thank you very much.