With recent updates to Jenkins or Java, the UI no longer shows when launching the JNLP file from a browser on the slave (orange launch button), or when running "javaws http://path/slave-agent.jnlp" on the slave from the command line.

Interestingly, the headless version does work, "java -jar slave.jar -jnlpUrl http://path/slave-agent.jnlp".

Global Security is not enabled so this does not appear to be a security issue (not to mention the headless version works).

Perhaps there is an issue with displaying the "Jenkins Slave Agent" window? There doesn't seem to be any error returned, but I note that after attempting a launch, Task Manager shows an instance of "Java Platform SE binary" remains running.