After upgrading from 1.500 to 1.503 the checkstyle report stopped working in all projects. I have since downgraded to 1.500 again but this didn't help. Nor have downgrading the static code analysis plugin helped. I keep getting this stack trace when restarting the server:

Feb 28, 2013 11:58:28 AM hudson.util.RobustCollectionConverter populateCollection
WARNING: Failed to resolve class
com.thoughtworks.xstream.mapper.CannotResolveClassException: hudson.plugins.checkstyle.CheckStyleMavenResultAction : hudson.plugins.checkstyle.CheckStyleMavenResultAction
at com.thoughtworks.xstream.mapper.DefaultMapper.realClass(DefaultMapper.java:68)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.DynamicProxyMapper.realClass(DynamicProxyMapper.java:71)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.PackageAliasingMapper.realClass(PackageAliasingMapper.java:88)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.ClassAliasingMapper.realClass(ClassAliasingMapper.java:86)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.ArrayMapper.realClass(ArrayMapper.java:96)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at hudson.util.XStream2$CompatibilityMapper.realClass(XStream2.java:231)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at hudson.util.xstream.MapperDelegate.realClass(MapperDelegate.java:43)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.CachingMapper.realClass(CachingMapper.java:56)
at com.thoughtworks.xstream.core.util.HierarchicalStreams.readClassType(HierarchicalStreams.java:29)
at com.thoughtworks.xstream.converters.collections.AbstractCollectionConverter.readItem(AbstractCollectionConverter.java:70)
at hudson.util.RobustCollectionConverter.populateCollection(RobustCollectionConverter.java:85)
at com.thoughtworks.xstream.converters.collections.CollectionConverter.unmarshal(CollectionConverter.java:61)
at hudson.util.RobustCollectionConverter.unmarshal(RobustCollectionConverter.java:76)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:82)
at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:63)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:76)
at hudson.util.RobustReflectionConverter.unmarshalField(RobustReflectionConverter.java:333)
at hudson.util.RobustReflectionConverter.doUnmarshal(RobustReflectionConverter.java:275)
at hudson.util.RobustReflectionConverter.unmarshal(RobustReflectionConverter.java:222)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:82)
at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:63)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:76)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:60)
at com.thoughtworks.xstream.core.TreeUnmarshaller.start(TreeUnmarshaller.java:137)
at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.unmarshal(AbstractTreeMarshallingStrategy.java:33)
at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:926)
at hudson.util.XStream2.unmarshal(XStream2.java:104)
at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:912)
at hudson.XmlFile.unmarshal(XmlFile.java:160)
at hudson.model.Run.reload(Run.java:307)
at hudson.model.Run.<init>(Run.java:296)
at hudson.model.AbstractBuild.<init>(AbstractBuild.java:180)
at hudson.maven.AbstractMavenBuild.<init>(AbstractMavenBuild.java:54)
at hudson.maven.MavenModuleSetBuild.<init>(MavenModuleSetBuild.java:135)
at sun.reflect.GeneratedConstructorAccessor36.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:532)
at hudson.model.AbstractProject.loadBuild(AbstractProject.java:1095)
at hudson.model.AbstractProject$1.create(AbstractProject.java:304)
at hudson.model.AbstractProject$1.create(AbstractProject.java:302)
at hudson.model.RunMap.retrieve(RunMap.java:225)
at hudson.model.RunMap.retrieve(RunMap.java:59)
at jenkins.model.lazy.AbstractLazyLoadRunMap.load(AbstractLazyLoadRunMap.java:646)
at jenkins.model.lazy.AbstractLazyLoadRunMap.load(AbstractLazyLoadRunMap.java:629)
at jenkins.model.lazy.AbstractLazyLoadRunMap.all(AbstractLazyLoadRunMap.java:581)
at jenkins.model.lazy.AbstractLazyLoadRunMap.entrySet(AbstractLazyLoadRunMap.java:243)
at java.util.AbstractMap$2$1.<init>(AbstractMap.java:378)
at java.util.AbstractMap$2.iterator(AbstractMap.java:377)
at hudson.util.RunList.iterator(RunList.java:103)
at org.jvnet.hudson.plugins.DownStreamProjectActionFactory.createFor(DownStreamProjectActionFactory.java:59)
at hudson.model.AbstractProject.createTransientActions(AbstractProject.java:709)
at hudson.maven.AbstractMavenProject.createTransientActions(AbstractMavenProject.java:177)
at hudson.maven.MavenModuleSet.createTransientActions(MavenModuleSet.java:448)
at hudson.model.AbstractProject.updateTransientActions(AbstractProject.java:699)
at hudson.maven.MavenModuleSet.updateTransientActions(MavenModuleSet.java:444)
at hudson.model.AbstractProject.onLoad(AbstractProject.java:298)
at hudson.maven.MavenModuleSet.onLoad(MavenModuleSet.java:746)
at hudson.model.Items.load(Items.java:221)
at jenkins.model.Jenkins$17.run(Jenkins.java:2540)
at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:146)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:259)
at jenkins.model.Jenkins$7.runTask(Jenkins.java:883)
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:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:679)

Feb 28, 2013 11:58:28 AM hudson.util.RobustCollectionConverter populateCollection
WARNING: Failed to resolve class
com.thoughtworks.xstream.mapper.CannotResolveClassException: hudson.plugins.checkstyle.CheckStyleReporter : hudson.plugins.checkstyle.CheckStyleReporter
at com.thoughtworks.xstream.mapper.DefaultMapper.realClass(DefaultMapper.java:68)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.DynamicProxyMapper.realClass(DynamicProxyMapper.java:71)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.PackageAliasingMapper.realClass(PackageAliasingMapper.java:88)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.ClassAliasingMapper.realClass(ClassAliasingMapper.java:86)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.ArrayMapper.realClass(ArrayMapper.java:96)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at hudson.util.XStream2$CompatibilityMapper.realClass(XStream2.java:231)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at hudson.util.xstream.MapperDelegate.realClass(MapperDelegate.java:43)
at com.thoughtworks.xstream.mapper.MapperWrapper.realClass(MapperWrapper.java:38)
at com.thoughtworks.xstream.mapper.CachingMapper.realClass(CachingMapper.java:56)
at com.thoughtworks.xstream.core.util.HierarchicalStreams.readClassType(HierarchicalStreams.java:29)
at com.thoughtworks.xstream.converters.collections.AbstractCollectionConverter.readItem(AbstractCollectionConverter.java:70)
at hudson.util.RobustCollectionConverter.populateCollection(RobustCollectionConverter.java:85)
at com.thoughtworks.xstream.converters.collections.CollectionConverter.unmarshal(CollectionConverter.java:61)
at hudson.util.RobustCollectionConverter.unmarshal(RobustCollectionConverter.java:76)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:82)
at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:63)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:76)
at hudson.util.RobustReflectionConverter.unmarshalField(RobustReflectionConverter.java:333)
at hudson.util.RobustReflectionConverter.doUnmarshal(RobustReflectionConverter.java:275)
at hudson.util.RobustReflectionConverter.unmarshal(RobustReflectionConverter.java:222)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convert(TreeUnmarshaller.java:82)
at com.thoughtworks.xstream.core.AbstractReferenceUnmarshaller.convert(AbstractReferenceUnmarshaller.java:63)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:76)
at com.thoughtworks.xstream.core.TreeUnmarshaller.convertAnother(TreeUnmarshaller.java:60)
at com.thoughtworks.xstream.core.TreeUnmarshaller.start(TreeUnmarshaller.java:137)
at com.thoughtworks.xstream.core.AbstractTreeMarshallingStrategy.unmarshal(AbstractTreeMarshallingStrategy.java:33)
at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:926)
at hudson.util.XStream2.unmarshal(XStream2.java:104)
at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:912)
at hudson.XmlFile.unmarshal(XmlFile.java:160)
at hudson.model.Run.reload(Run.java:307)
at hudson.model.Run.<init>(Run.java:296)
at hudson.model.AbstractBuild.<init>(AbstractBuild.java:180)
at hudson.maven.AbstractMavenBuild.<init>(AbstractMavenBuild.java:54)
at hudson.maven.MavenBuild.<init>(MavenBuild.java:110)
at sun.reflect.GeneratedConstructorAccessor43.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:532)
at hudson.model.AbstractProject.loadBuild(AbstractProject.java:1095)
at hudson.model.AbstractProject$1.create(AbstractProject.java:304)
at hudson.model.AbstractProject$1.create(AbstractProject.java:302)
at hudson.model.RunMap.retrieve(RunMap.java:225)
at hudson.model.RunMap.retrieve(RunMap.java:59)
at jenkins.model.lazy.AbstractLazyLoadRunMap.load(AbstractLazyLoadRunMap.java:646)
at jenkins.model.lazy.AbstractLazyLoadRunMap.load(AbstractLazyLoadRunMap.java:629)
at jenkins.model.lazy.AbstractLazyLoadRunMap.all(AbstractLazyLoadRunMap.java:581)
at jenkins.model.lazy.AbstractLazyLoadRunMap.entrySet(AbstractLazyLoadRunMap.java:243)
at java.util.AbstractMap$2$1.<init>(AbstractMap.java:378)
at java.util.AbstractMap$2.iterator(AbstractMap.java:377)
at hudson.util.RunList.iterator(RunList.java:103)
at org.jvnet.hudson.plugins.DownStreamProjectActionFactory.createFor(DownStreamProjectActionFactory.java:59)
at hudson.model.AbstractProject.createTransientActions(AbstractProject.java:709)
at hudson.maven.AbstractMavenProject.createTransientActions(AbstractMavenProject.java:177)
at hudson.model.AbstractProject.updateTransientActions(AbstractProject.java:699)
at hudson.maven.MavenModule.updateTransientActions(MavenModule.java:411)
at hudson.model.AbstractProject.onLoad(AbstractProject.java:298)
at hudson.maven.MavenModule.onLoad(MavenModule.java:236)
at hudson.model.Items.load(Items.java:221)
at hudson.model.ItemGroupMixIn.loadChildren(ItemGroupMixIn.java:99)
at hudson.maven.MavenModuleSet.onLoad(MavenModuleSet.java:748)
at hudson.model.Items.load(Items.java:221)
at jenkins.model.Jenkins$17.run(Jenkins.java:2540)
at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:146)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:259)
at jenkins.model.Jenkins$7.runTask(Jenkins.java:883)
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:1110)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
at java.lang.Thread.run(Thread.java:679)