I just upgraded to Hudson 1.321 and TFS plugin 1.8 today. Polling no longer
works, and my error log is filled up with errors like this:

Aug 27, 2009 11:46:09 AM hudson.triggers.SCMTrigger$Runner runPolling
SEVERE: Failed to record SCM polling
java.lang.NullPointerException
at hudson.plugins.tfs.TfTool.execute(TfTool.java:99)
at hudson.plugins.tfs.model.Server.execute(Server.java:47)
at hudson.plugins.tfs.model.Project.getDetailedHistory(Project.java:41)
at
hudson.plugins.tfs.TeamFoundationServerScm.pollChanges(TeamFoundationServerScm.java:187)
at hudson.model.AbstractProject.pollSCMChanges(AbstractProject.java:965)
at hudson.triggers.SCMTrigger$Runner.runPolling(SCMTrigger.java:312)
at hudson.triggers.SCMTrigger$Runner.run(SCMTrigger.java:339)
at
hudson.util.SequentialExecutionQueue$QueueEntry.run(SequentialExecutionQueue.java:114)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:417)
at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:269)
at java.util.concurrent.FutureTask.run(FutureTask.java:123)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:650)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:675)
at java.lang.Thread.run(Thread.java:595)

I reverted to TFS plugin version "1.6-SNAPSHOT (private-06/08/2009
07:32-hudson)" which I had downloaded from your site, but that did not resolve
the problem.

I reverted to the previous version of Hudson I had been using (1.318) and the
problem was resolved. I'll try upgrading to TFS plugin 1.8 again and see if the
problem reoccurs.

But it appears a change in Hudson between 1.318 and 1.321 is causing this problem.