Follow the link in you error to see a list of potential issues. Did you verify that a connection to jfrog artifactory can be established from your build server and the dependency is hosted by your artifactory?

BTW the mentioned artifact org.apache.activemq:activemq-pool:jar:5.7.0 was released on Oct 02, 2012. Are you sure you want to build on such an outdated library instead of using a newer version (like 6.1.6)?