On a Windows 10 system, I can connect my Jenkins slave through the command line but not via Services.
jenkins-slave.err.log shows MalformedByteSequence: invalid byte 2 of 2-byte UTF-8 sequence
MalformedByteSequenceException explained why it happens (and saved me the headache of transcribing the traceback stack!), but not how to find where the problem is so that I can fix it.
In a browser, I entered http://my-jenkins-master:8080/computer/my_agent/slave-agent.jnlp
Got the dialog window You have chose to open slave-agent.jnlp with size 377 bytes
But when I select "Save File" -- nothing happens, and jenkins-slave.err.log shows Content is not allowed in prolog
Other agents can download their slave-agent.jnlp OK, so I don't know where the problem is so that I can fix it.
Will be glad to supply any other information you need.