Our jobs are failing with the following stacktrace.
We have a master/slave setup (linux master and in this case a linux slave connected via ssh).
It is just a free job.

Recording test results
[PMD] Collecting PMD analysis files...
FATAL: remote file operation failed
hudson.util.IOException2: remote file operation failed
at hudson.FilePath.act(FilePath.java:677)
at hudson.FilePath.act(FilePath.java:665)
at hudson.plugins.pmd.PmdPublisher.perform(PmdPublisher.java:103)
at hudson.plugins.analysis.core.HealthAwarePublisher.perform(HealthAwarePublisher.java:140)
at hudson.tasks.BuildStepMonitor$2.perform(BuildStepMonitor.java:27)
at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:577)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildStep(AbstractBuild.java:563)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildStep(AbstractBuild.java:551)
at hudson.model.Build$RunnerImpl.post2(Build.java:152)
at hudson.model.AbstractBuild$AbstractRunner.post(AbstractBuild.java:535)
at hudson.model.Run.run(Run.java:1199)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:123)
Caused by: java.io.IOException: Remote call failed
at hudson.remoting.Channel.call(Channel.java:552)
at hudson.FilePath.act(FilePath.java:672)
... 13 more
Caused by: java.lang.ClassNotFoundException: Failed to deserialize the Callable object. Perhaps you needed to implement DelegatingCallable?
at hudson.remoting.UserRequest.perform(UserRequest.java:90)
at hudson.remoting.UserRequest.perform(UserRequest.java:48)
at hudson.remoting.Request$2.run(Request.java:270)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.ClassNotFoundException: hudson.plugins.pmd.parser.PmdParser
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:303)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:316)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:247)
at java.io.ObjectInputStream.resolveClass(ObjectInputStream.java:604)
at hudson.remoting.ObjectInputStreamEx.resolveClass(ObjectInputStreamEx.java:50)
at java.io.ObjectInputStream.readNonProxyDesc(ObjectInputStream.java:1575)
at java.io.ObjectInputStream.readClassDesc(ObjectInputStream.java:1496)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1732)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1329)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1947)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1871)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1753)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1329)
at java.io.ObjectInputStream.defaultReadFields(ObjectInputStream.java:1947)
at java.io.ObjectInputStream.readSerialData(ObjectInputStream.java:1871)
at java.io.ObjectInputStream.readOrdinaryObject(ObjectInputStream.java:1753)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1329)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:351)
at hudson.remoting.UserRequest.deserialize(UserRequest.java:168)
at hudson.remoting.UserRequest.perform(UserRequest.java:88)
... 8 more