Depends on what you want to do. If this is a PSTN call, you cannot block a specific call at the IP phone level. In this case, you would need to use an H323 configuration where you can configure a blacklist and block calls based on caller ID.
If you want to block User A from calling User B, you would need to leverage partition and CSS setup to do this - however, this is rarely done for one specific caller.
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.