When users try to log in to Library application, they face following error: "PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target".

Intelligence Server is connected properly in the Strategy Library Admin page.
By default, REST API port 34962 is necessary for connectivity between Library server and Intelligence Server machine – in this case we face an issue due to a protocol mismatch. The reason for that is because Intelligence Server has TLS enabled, but Library application does not use it. At the same time, REST API port expects for the communication to happen over a secure channel since it is set on the I-Server side, which results in an error.
There are two ways to overcome this issue:
• If TLS is not needed, disable TLS on the Intelligence Server, in the server definition.
• If TLS is required- configure Library to use TLS when communicating with Intelligence Server.