When upgrading jenkins from 1.523 to 1.524, jenkins crashes. In the web interface, all I see is the error below.

Restoring the old version:
mv jenkins.war jenkins.war2
cp jenkins.war.bak jenkins.war

makes it work again. Any idea what the problem could be?

—

org.jvnet.hudson.reactor.ReactorException: java.lang.Error: java.lang.reflect.InvocationTargetException
at org.jvnet.hudson.reactor.Reactor.execute(Reactor.java:246)
at jenkins.InitReactorRunner.run(InitReactorRunner.java:43)
at jenkins.model.Jenkins.executeReactor(Jenkins.java:906)
at jenkins.model.Jenkins.<init>(Jenkins.java:806)
at hudson.model.Hudson.<init>(Hudson.java:81)
at hudson.model.Hudson.<init>(Hudson.java:77)
at hudson.WebAppMain$2.run(WebAppMain.java:214)
Caused by: java.lang.Error: java.lang.reflect.InvocationTargetException
at hudson.init.InitializerFinder.invoke(InitializerFinder.java:124)
at hudson.init.InitializerFinder$TaskImpl.run(InitializerFinder.java:184)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:259)
at jenkins.model.Jenkins$7.runTask(Jenkins.java:895)
at org.jvnet.hudson.reactor.Reactor$2.run(Reactor.java:187)
at org.jvnet.hudson.reactor.Reactor$Node.run(Reactor.java:94)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:724)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at hudson.init.InitializerFinder.invoke(InitializerFinder.java:120)
... 8 more
Caused by: java.lang.NoClassDefFoundError: hudson/maven/MavenModule
at hudson.plugins.jobConfigHistory.JobConfigHistory.isSaveable(JobConfigHistory.java:426)
at hudson.plugins.jobConfigHistory.JobConfigHistorySaveableListener.onChange(JobConfigHistorySaveableListener.java:28)
at hudson.model.listeners.SaveableListener.fireOnChange(SaveableListener.java:78)
at hudson.model.UpdateCenter.save(UpdateCenter.java:519)
at hudson.util.PersistedList.onModified(PersistedList.java:173)
at hudson.util.PersistedList.replaceBy(PersistedList.java:85)
at hudson.model.UpdateCenter.load(UpdateCenter.java:533)
at hudson.model.UpdateCenter.init(UpdateCenter.java:1546)
... 13 more
Caused by: java.lang.ClassNotFoundException: hudson.maven.MavenModule
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 21 more