This can also happen when your modeler has crashed. It hasn't properly killed the old process running on that thread.
You could also try to do the following described here: https://stackoverflow.com/questions/39632667/how-can-i-close-some-specific-port-on-linux
It says linux in the title, but it works on windows too.
This allows you to see what is running and kill it, always works for me! Hope this helps!
Hi Park
You can update the server URL in your configuration settings
Ref: