This plugin worked fine for me with Jenkins 1.65.

I recently upgraded to Jenkins 2.51, and everything is working on the new server except monitored remote jobs. 

To install the plugin, I extracted the following jar files from the war file and installed them on the remote system as instructed on the plugin wiki. 

{{jenkins-core-*.jar }}

{{remoting-*.jar }}

{{ant-1.7.0.jar }}

{{commons-io-1.4jar }}

{{commons-lang-2.4.jar }}

{{jna-posix-*.jar }}

xstream-*.jar

The remote system has java 1.7.0_131.

Now when I try to run the cron jobs on the remote system using the jenkins-core.jar, it fails with this trace:
 
Exception in thread "main" java.lang.NoClassDefFoundError: javax/servlet/ServletContextListener
                at java.lang.ClassLoader.defineClass1(Native Method)
                at java.lang.ClassLoader.defineClass(ClassLoader.java:803)
                at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
                at java.net.URLClassLoader.defineClass(URLClassLoader.java:442)
                at java.net.URLClassLoader.access$100(URLClassLoader.java:64)
                at java.net.URLClassLoader$1.run(URLClassLoader.java:354)
                at java.net.URLClassLoader$1.run(URLClassLoader.java:348)
                at java.security.AccessController.doPrivileged(Native Method)
                at java.net.URLClassLoader.findClass(URLClassLoader.java:347)
                at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
                at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
                at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
                at hudson.Main.<clinit>(Main.java:222)
Caused by: java.lang.ClassNotFoundException: javax.servlet.ServletContextListener
                at java.net.URLClassLoader$1.run(URLClassLoader.java:359)
                at java.net.URLClassLoader$1.run(URLClassLoader.java:348)
                at java.security.AccessController.doPrivileged(Native Method)
                at java.net.URLClassLoader.findClass(URLClassLoader.java:347)
                at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
                at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
                at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
                ... 13 more
 

None of the jar files contain ServletContextListener.  From google I learn it is in the servlet api so I found the servlet-api-2.5.jar on Oracle's website and tried putting that in the same directory as the other jar files, and setting CLASSPATH, but the same error occurs.

Is this a problem with the plugin or its documentation?