Sometimes a port doesn't release properly resulting in servers starting on non-standard ports.

How do you release the port? Easy, use this:

lsof -i :portnumber

Grab the resulting PID and kill the process. Use -9 if you really have to.

Here's a "worked example":

$ lsof -i :1990

COMMAND  PID  USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME

java    2857 david   39u  IPv6 0x23ed6292526f5971      0t0  TCP *:stun-p1 (LISTEN)

$ kill -9 2857