I believe CUCM 8.5.1 introduces the 64 bit TSP and is included in every version onward. What version did you upgrade from? Depending on that, you could simply do a switch version back to the old version sitting on the inactive partition. Please keep in mind that if you do revert back to an older version, you must reset database replication.
Yes you can. After upgrading to 9.1 you will be able to do a switch version back to the inactive partition that is housing your previous version 8.0.3. Again, if you do revert back to 8.0 you will have to reset database replication.
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.