My jobs failed when processing CppUnit with this error :

ERROR: Publisher org.jenkinsci.plugins.xunit.XUnitPublisher aborted due to exception
hudson.util.IOException2: remote file operation failed: /var/jenkins/workspace/nameOfMyJob at hudson.remoting.Channel@cb61b:runner-rh4u8
at hudson.FilePath.act(FilePath.java:838)
at hudson.FilePath.act(FilePath.java:824)
at org.jenkinsci.plugins.xunit.XUnitPublisher.performTests(XUnitPublisher.java:170)
at org.jenkinsci.plugins.xunit.XUnitPublisher.performXUnit(XUnitPublisher.java:115)
at org.jenkinsci.plugins.xunit.XUnitPublisher.perform(XUnitPublisher.java:92)
at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:19)
at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:717)
at hudson.model.AbstractBuild$AbstractBuildExecution.performAllBuildSteps(AbstractBuild.java:692)
at hudson.model.Build$BuildExecution.post2(Build.java:183)
at hudson.model.AbstractBuild$AbstractBuildExecution.post(AbstractBuild.java:639)
at hudson.model.Run.execute(Run.java:1513)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:236)
Caused by: java.io.IOException: Remote call on runner-rh4u8 failed
at hudson.remoting.Channel.call(Channel.java:672)
at hudson.FilePath.act(FilePath.java:831)
... 13 more
Caused by: java.lang.ClassFormatError: Failed to load com.thalesgroup.dtkit.junit.CppUnit
at hudson.remoting.RemoteClassLoader.loadClassFile(RemoteClassLoader.java:154)
at hudson.remoting.RemoteClassLoader.findClass(RemoteClassLoader.java:131)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at hudson.remoting.MultiClassLoaderSerializer$Input.resolveClass(MultiClassLoaderSerializer.java:113)
at java.io.ObjectInputStream.readNonProxyDesc(Unknown Source)
at java.io.ObjectInputStream.readClassDesc(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.defaultReadFields(Unknown Source)
at java.io.ObjectInputStream.readSerialData(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.defaultReadFields(Unknown Source)
at java.io.ObjectInputStream.readSerialData(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.defaultReadFields(Unknown Source)
at java.io.ObjectInputStream.readSerialData(Unknown Source)
at java.io.ObjectInputStream.readOrdinaryObject(Unknown Source)
at java.io.ObjectInputStream.readObject0(Unknown Source)
at java.io.ObjectInputStream.readObject(Unknown Source)
at hudson.remoting.UserRequest.deserialize(UserRequest.java:182)
at hudson.remoting.UserRequest.perform(UserRequest.java:98)
at hudson.remoting.UserRequest.perform(UserRequest.java:48)
at hudson.remoting.Request$2.run(Request.java:326)
at hudson.remoting.InterceptingExecutorService$1.call(InterceptingExecutorService.java:72)
at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.UnsupportedClassVersionError: Bad version number in .class file
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.lang.ClassLoader.defineClass(Unknown Source)
at hudson.remoting.RemoteClassLoader.loadClassFile(RemoteClassLoader.java:152)
... 34 more

I can't find why this happens. I have a master/slave configuration, jenkins master is on ubuntu and jenkins slave (named runner-rh4u8 in traces above) on redhat4 update8

Thanks in advance for your help