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Listener unable to access port

Wake-on-LAN uses UDP port 9 by default, to send WOL messages. This port is available for use on most Windows computers. However, if you have installed "Simple TCPIP services", then Windows may be running the "discard" service. This service locks port 9 and will prevent the listener from connecting.

Go to Control Panel and disable the "Simple TCP/IP Services" service. You should now be able to run WOL without any conflict. If you suspect another program is using port 9, you can run netstat to find out which application has the port locked. The command "Netstat -ab" will list all of the ports that are in use. This must be run as Administrator. Look for the line following UDP 0.0.0.0:9. That will be the name of the application that is using port 9.