Trying to use scons plugin with latest jenkins 1.412 causes fatal exception:

18-May-2011 12:56:57 hudson.util.CopyOnWriteList$ConverterImpl unmarshal
WARNING: Failed to resolve class
com.thoughtworks.xstream.mapper.CannotResolveClassException: com.thalesgroup.hudson.plugins.scons.SConsBuilderScriptFile : com.thalesgroup.hudson.plugins.scons.SConsBuilderScriptFile
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:142)
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.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.CopyOnWriteList$ConverterImpl.unmarshal(CopyOnWriteList.java:189)
at hudson.util.DescribableList$ConverterImpl.unmarshal(DescribableList.java:245)
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 hudson.util.RobustReflectionConverter.unmarshalField(RobustReflectionConverter.java:290)
at hudson.util.RobustReflectionConverter.doUnmarshal(RobustReflectionConverter.java:233)
at hudson.util.RobustReflectionConverter.unmarshal(RobustReflectionConverter.java:180)
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:80)
at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:912)
at com.thoughtworks.xstream.XStream.fromXML(XStream.java:856)
at hudson.XmlFile.read(XmlFile.java:126)
at hudson.model.Items.load(Items.java:113)
at hudson.model.Hudson$13.run(Hudson.java:2354)
at org.jvnet.hudson.reactor.TaskGraphBuilder$TaskImpl.run(TaskGraphBuilder.java:146)
at org.jvnet.hudson.reactor.Reactor.runTask(Reactor.java:259)
at hudson.model.Hudson$4.runTask(Hudson.java:735)
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:636)

I tried to google for similar issues, but couldn't really find any clue to why this is happening.