There was no endpoint listening at http://ServerName:5725 ResourceManagementService/MEX that could accept the message. This is often caused by an incorrect address or SOAP action. See InnerException, if present, for more details

Error Occurred when Creating a New Connection in SharePoint User Profile Service Application.

There was no endpoint listening at http://ServerName:5725 ResourceManagementService/MEX that could accept the message. This is often caused by an incorrect address or SOAP action. See InnerException, if present, for more details.

Quite scary error which seems like due to ports blocking ? Not really, In my case it was Forefront Identity Manager Service which was stopped.

I remember that I restarted this server after doing some heavy site collections creation and noticed the FIM Service has not been started automatically though it was set to automatic start. Just started it from Services and Connection came back to work.

You will get "LDAP Server is Unavailable" Massage if you have checked SSL option at the same page (will depend on the environment that you are dealing with).