Did you check if you have a Conference bridge configured on CCM?
Also, if you are running out of software conference sessions, you can increase them, just go to service >> service parameters and select the server and the Cisco IP Voice Media Streaming App service, there you will see the conf session number.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.