My Jenkins is on the LTS release. I just upgraded it from 1.480.3 to 1.509.1. Now none of my SSH slaves work. They fail to start and the log contains the following:

[05/03/13 09:11:05] [SSH] Opening SSH connection to ###.local:22.

ERROR: Unexpected error in launching a slave. This is probably a bug in Jenkins.
java.lang.NoSuchMethodError: com.cloudbees.jenkins.plugins.sshcredentials.SSHAuthenticator.authenticate(Lhudson/model/TaskListener;)Z
at hudson.plugins.sshslaves.SSHLauncher.openConnection(SSHLauncher.java:918)
at hudson.plugins.sshslaves.SSHLauncher.launch(SSHLauncher.java:479)
at hudson.slaves.SlaveComputer$1.call(SlaveComputer.java:222)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
at java.util.concurrent.FutureTask.run(FutureTask.java:166)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1146)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:679)
[05/03/13 09:11:05] [SSH] Connection closed.