. I see now that's a tough thing to figure out.
Actually, you can find out pretty easily do it from the Terminal.
Restart your machine and open a Terminal window. (Don't open Isadora!)
Enter the following command.lsof -i4UDP:1234
and hit return. The result will show you what process is using the port. When Isadora is running on my machine, it saysCOMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME Isadora 1073 mconiglio 42u IPv4 0xd3288f011e6d613d 0t0 UDP *:search-agent
If the process using the command is mysterious, you can try using Activity Monitor to look for the matching PID (Process Identifier) number.