A full build (triggered from web page) works. When it is set up to run every 30 minutes I get the following error whether there are changes in PVCS or not:

INFO: looking for changes between Mon Dec 06 10:05:21 EST 2010 and Mon Dec 06 14:31:03 EST 2010
Dec 6, 2010 2:31:03 PM hudson.triggers.SCMTrigger$Runner runPolling
SEVERE: Failed to record SCM polling
java.lang.NullPointerException
at hudson.plugins.pvcs_scm.PvcsScm.getModifications(PvcsScm.java:419)
at hudson.plugins.pvcs_scm.PvcsScm.pollChanges(PvcsScm.java:337)
at hudson.scm.SCM.poll(SCM.java:373)
at hudson.model.AbstractProject.poll(AbstractProject.java:1250)
at hudson.triggers.SCMTrigger$Runner.runPolling(SCMTrigger.java:425)
at hudson.triggers.SCMTrigger$Runner.run(SCMTrigger.java:454)
at hudson.util.SequentialExecutionQueue$QueueEntry.run(SequentialExecutionQueue.java:118)
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

If I run the command that is genterates (based on finest logging) the command runs and either returns nothing or returns a change report. In either case, the NPE is generated.