Thanks for your answer. This seems to be a good idea.
I wonder if there is a document showing compatibility between firware 8.4.1 and CUCM 8.5 ?
In fact the biggest problem to do such a revert is the trust list downloaded by the Phone while it is upgrading and registering on the CUCM8. Is there an automatic way to erase the trust list ? or to put the files on CCM4.X TFTP ?
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.