It should be enabled by default as far as I am aware.
When you place a second call to a phone the user should see it presented on the display and then needs to answer it by using the toggle button. If the user fails to do this before the CFNA timer expires the call will be forwarded to the CNFA destination (usually voiemail).
Is this what is happening or does the second caller get forwarded as soon as the call is placed? (i.e. they do not hear ringback at all).
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.