I upgraded to 1.9 this morning and restarted hudson. All of the projects which
used tasks were not visible on the dashboard. Looking into the logs there was
an exception for each project which used tasks. (See stacktrace at bottom of
issue.)

I tried removing the task config from the config.xml for one of the projects,
restarted hudson, and the project loaded successfully.

I then tried rolling back to the 1.8 version of the batch-task plugin, restarted
hudson, and all of the projects loaded successfully and appeared in the dashboard.

Stack trace for the first project which did not load:
Running from: /app/buildenv/hudson/hudson.war
[Winstone 2009/11/11 21:03:45] - Beginning extraction from war file
hudson home directory: /app/buildenv/hudson/home
[Winstone 2009/11/11 21:03:49] - HTTP Listener started: port=8087
[Winstone 2009/11/11 21:03:49] - Winstone Servlet Engine v0.9.10 running:
controlPort=disabled
Nov 11, 2009 9:03:50 PM hudson.ClassicPluginStrategy createPluginWrapper
INFO: Loading plugin: /app/buildenv/hudson/home/plugins/maven-plugin.hpi
Nov 11, 2009 9:03:50 PM hudson.ClassicPluginStrategy createPluginWrapper
INFO: Loading plugin: /app/buildenv/hudson/home/plugins/subversion.hpi
Nov 11, 2009 9:03:50 PM hudson.ClassicPluginStrategy createPluginWrapper
INFO: Loading plugin: /app/buildenv/hudson/home/plugins/scis-ad.hpi
Nov 11, 2009 9:03:50 PM hudson.ClassicPluginStrategy createPluginWrapper
INFO: Loading plugin: /app/buildenv/hudson/home/plugins/ssh-slaves.hpi
Nov 11, 2009 9:03:50 PM hudson.ClassicPluginStrategy createPluginWrapper
INFO: Loading plugin: /app/buildenv/hudson/home/plugins/batch-task.hpi
Nov 11, 2009 9:03:50 PM hudson.ClassicPluginStrategy createPluginWrapper
INFO: Loading plugin: /app/buildenv/hudson/home/plugins/cvs-tag.hpi
Nov 11, 2009 9:03:50 PM hudson.ClassicPluginStrategy createPluginWrapper
INFO: Loading plugin: /app/buildenv/hudson/home/plugins/setenv.hpi
Nov 11, 2009 9:03:50 PM hudson.ClassicPluginStrategy createPluginWrapper
INFO: Loading plugin: /app/buildenv/hudson/home/plugins/audit-trail.hpi
Nov 11, 2009 9:03:51 PM hudson.model.Hudson load
INFO: Loading in 64 parallel threads
Nov 11, 2009 9:03:58 PM hudson.model.Hudson load
WARNING: Failed to load a project
hudson.util.IOException2: Unable to read
/app/buildenv/hudson/home/jobs/markets-ticketprinting/config.xml
at hudson.XmlFile.read(XmlFile.java:132)
at hudson.model.Items.load(Items.java:106)
at hudson.model.Hudson$9.call(Hudson.java:2008)
at hudson.model.Hudson$9.call(Hudson.java:2001)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
at java.util.concurrent.FutureTask.run(FutureTask.java:138)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
at java.lang.Thread.run(Thread.java:619)
Caused by: java.lang.NoClassDefFoundError: hudson/model/queue/CauseOfBlockage
at java.lang.Class.getDeclaredMethods0(Native Method)
at java.lang.Class.privateGetDeclaredMethods(Class.java:2427)
at java.lang.Class.getDeclaredMethod(Class.java:1935)
at
com.thoughtworks.xstream.converters.reflection.SerializationMethodInvoker.getMethod(SerializationMethodInvoker.java:128)
at
com.thoughtworks.xstream.converters.reflection.SerializationMethodInvoker.callReadResolve(SerializationMethodInvoker.java:43)
at
hudson.util.RobustReflectionConverter.unmarshal(RobustReflectionConverter.java:174)
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.converters.collections.AbstractCollectionConverter.readItem(AbstractCollectionConverter.java:71)
at
com.thoughtworks.xstream.converters.collections.ArrayConverter.unmarshal(ArrayConverter.java:55)
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.unmarshallField(RobustReflectionConverter.java:262)
at
hudson.util.RobustReflectionConverter.doUnmarshal(RobustReflectionConverter.java:222)
at
hudson.util.RobustReflectionConverter.unmarshal(RobustReflectionConverter.java:173)
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.converters.collections.AbstractCollectionConverter.readItem(AbstractCollectionConverter.java:71)
at
hudson.util.CopyOnWriteList$ConverterImpl.unmarshal(CopyOnWriteList.java:184)
at
hudson.util.CopyOnWriteList$ConverterImpl.unmarshal(CopyOnWriteList.java:163)
at hudson.util.XStream2$AssociatedConverterImpl.unmarshal(XStream2.java:151)
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.unmarshallField(RobustReflectionConverter.java:262)
at
hudson.util.RobustReflectionConverter.doUnmarshal(RobustReflectionConverter.java:222)
at
hudson.util.RobustReflectionConverter.unmarshal(RobustReflectionConverter.java:173)
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:923)
at hudson.util.XStream2.unmarshal(XStream2.java:67)
at com.thoughtworks.xstream.XStream.unmarshal(XStream.java:909)
at com.thoughtworks.xstream.XStream.fromXML(XStream.java:853)
at hudson.XmlFile.read(XmlFile.java:126)
... 8 more
Caused by: java.lang.ClassNotFoundException: hudson.model.queue.CauseOfBlockage
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
... 53 more
Nov 11, 2009 9:03:58 PM hudson.model.Hudson load