Why do I get a "Port already listening" SocketException when calling listen()?

A java.net.SocketException "Port already listening" is thrown by TransportMapping.listen() (or Snmp.listen()) if that listen() method has been called before without an intermediate TransportMapping.close() call. That is, you tried to put the transport mapping into listen mode twice.

See also: Can I use a TransportMapping with two Snmp instances?