CA Release Automation v5.x and above.
In this case the artifact retrieval agent was setup to pull the file from an https URL. For this to work the artifact retrieval agent needs the certificate for that https site imported into its java keystore. The nolio_all.log file from the artifact retrieval agent confirms the cause and will general the following error message when it tries to access an https site that it doesnot have a certificate for (needed to establish a proper SSL handshake):
2018-06-26 10:40:58,617 [ArtifactsHandlers-1] DEBUG (com.nolio.platform.shared.datamodel.Action:167) - Accessing URL [https://yourUrl/path/to/file] with parameters [],
2018-06-26 10:40:58,758 [ArtifactsHandlers-1] ERROR (com.nolio.platform.shared.datamodel.Action:181) - exception caught
javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target