After installing the 'BMC CI Viewer' for CMDB 2.0,
I got the message: "CMDB libraries are not available. Please install the CI Relationship Viewer on the Mid Tier Server" when I tried to use it.

Could someone advise me on what to get the 'BMC CI Viewer' useful.

If you are using Tomcat, go to your Tomcat Manager, delete the /arsys context and deploy the /arsys context...

Then restart your Tomcat server and enjoy