Universal Plugin Manager 2.0 : Upgrade tab shows java.net.ConnectException

If you see an error box on the upgrade tab containing the message java.net.ConnectException: Connection refused: connect, your host application server may be having trouble contacting http://plugins.atlassian.com. This may be a problem with your application's proxy settings.

Note: the Universal Plugin Manager will access and use the proxy settings of the host application. See documentation for :

as well as UPM-693