One most probable reason is your MCU might be trying to register with multiple h323 id's and that is what is causing the problem. This MCU should only register with one h323 id, and it is possible to configure zone prefizes or gw-type prefixes to route the particular prefixes to that gateway.
Second probable reason is MCU registration entry is predefined at gatekeeper. Delete it and try to register. Another possible solution is set mode of MCU to GW, then reset it and try to register.
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.