It works fine with Jenkins 1.529, but after auto update to 1.530, it failed to load.

Sep 25, 2013 9:57:05 AM jenkins.InitReactorRunner$1 onTaskFailed
SEVERE: Failed Loading plugin disk-usage
hudson.util.IOException2: Unable to load hudson.plugins.disk_usage.DiskUsagePlugin from disk-usage
at hudson.ClassicPluginStrategy.load(ClassicPluginStrategy.java:352)
at hudson.PluginManager$2$1$1.run(PluginManager.java:355)
at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:146)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:259)
at jenkins.model.Jenkins$7.runTask(Jenkins.java:899)
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(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.NoClassDefFoundError: hudson/maven/MavenBuild
at hudson.plugins.disk_usage.DiskUsagePlugin.<init>(DiskUsagePlugin.java:29)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at java.lang.Class.newInstance0(Unknown Source)
at java.lang.Class.newInstance(Unknown Source)
at hudson.ClassicPluginStrategy.load(ClassicPluginStrategy.java:346)
... 9 more
Caused by: java.lang.ClassNotFoundException: hudson.maven.MavenBuild
at org.apache.tools.ant.AntClassLoader.findClassInComponents(AntClassLoader.java:1365)
at org.apache.tools.ant.AntClassLoader.findClass(AntClassLoader.java:1315)
at org.apache.tools.ant.AntClassLoader.loadClass(AntClassLoader.java:1068)
at java.lang.ClassLoader.loadClass(Unknown Source)
... 17 more