The server rejected the connection: None of the protocols were accepted

In my case that was linked to disabled protocol.

Check next: If your Jenkins is supporting JNLPv4, enable it before use.

Jenkins -> Global Security Configuration -> Agents -> Agent protocols -> Inbound TCP Agent Protocol/4 (TLS encryption)

The issue is from JENKINS side.The Bug is already raised on JENKINS Forum & Status is still Critical & Unresolved :

https://issues.jenkins-ci.org/browse/JENKINS-29616

As Per the Description :

A scheduled batch is attempting to start the slave agent with the following script:

taskkill /f /im "EXCEL.exe"taskkill /f /im "ipy.exe"taskkill /f /im "jp2launcher.exe"javaws http://172.16.8.57:8080/computer/SSW73210/slave-agent.jnlp

When the slave agent opens, it fails to do anything but the enclosed error. After rebooting, this issue fails to reproduce, but this seems dramatically more common when the slave is left on overnight.

I had a similar issue, here is what I did to resolve mine:

After upgrading from Jenkins 1.x to 2.x I never cleared the remote root directory of the slaves (in my case c:\jenkins). Everytime I installed the slave as a service I would get the exact same error. I finally figured out my problem after numerous grey hair:Once I removed the contents from that directory, and installed the jenkins slave as a windows service, the contents were repopulated and the slave connected as expected.

Hope this helps