Description:
EMS server is started with listener port as following:
listen    = tcp://8222
or
listen = tcp://localhost:8222

EMS admin client will fail to connect to the local EMS server using the following connect option:
using port only e.g. "connect 7204"
or
using localhost e.g "tcp://localhost:7204"
Symptoms:
This may happen to the EMS admin client after 6.3 version which provides support for IPv6 (Linux and Windows) and the machine has IPV 6 disabled.

Cause:
EMS uses getaddreinfo()  to return all loopback addresses. It also returns IPV6 loopback addresses even if IPV 6 is enabled.

The following JIRA issue was logged which will be addressed in a future release:
EMS-6194
EMS should abort the connection attempt when connect() returns anything but OK or EINPROGRESS for non blocking sockets.

EMS admin client fails to connect to the local EMS server using the following connect option: using port only e.g. "connect 7204" or using localhost e.g "tcp://localhost:7204"

Enable IPV 6 or use the specific hostname or IP address for listening/connecting from/to the EMS server.