Your comments

Thank you for your reply! I have tried it today with same result.

You are right with network problem: If I run with stacktrace option, the message is "Caused by: org.apache.http.ProtocolException: The server failed to respond with a valid HTTP response ...". But if I copy the URL http://repository-javafx-gradle-plugin.forge.cloudbees.com/snapshot/org/bitbucket/shemnon/javafxplugin/gradle-javafx-plugin/8.1.2-SNAPSHOT/gradle-javafx-plugin-8.1.2-20141008.214348-1.pom to my Browser, I can read the *.pom. Now I tried another network, wich is not secured with firewall - this error not appear. In our firewall the http protocol and port is open, also for https! Can you say, what other I must consider?