• The listener has not been started on the remote system.
• The connection name in the client channel definition is incorrect.
• The network is currently unavailable.
• A firewall blocking the port, or protocol-specific traffic.
• The security call initializing the IBM® WebSphere® MQ client is blocked by a security exit on the SVRCONN channel at the server

Try following steps to fix this error.

• Make sure the queue manager is started and running.
• Check the listener status and make sure it's running.
• Check the network connection from Adapter machine to the MQ server make sure the connection is fine.
• If there's firewall in between, turn off firewall to do a test. Or review the policy to make sure the connection to the MQ server and port is not blocked.