Error sending mails: cli to get mvn version return code 1

Any idea why I get this error sometimes

2012-04-12 00:00:38,541 [pool-1-thread-15] ERROR org.apache.maven.continuum.notification.DefaultContinuumNotificationDispatcher - Error while trying to use the mail notifier.
org.apache.maven.continuum.notification.NotificationException: Error while generating mail contents.
at org.apache.maven.continuum.notification.mail.MailContinuumNotifier.buildComplete(MailContinuumNotifier.java:409)
at org.apache.maven.continuum.notification.mail.MailContinuumNotifier.buildComplete(MailContinuumNotifier.java:306)
at org.apache.maven.continuum.notification.mail.MailContinuumNotifier.sendMessage(MailContinuumNotifier.java:280)
at org.apache.maven.continuum.notification.DefaultContinuumNotificationDispatcher.sendNotification(DefaultContinuumNotificationDispatcher.java:194)
at org.apache.maven.continuum.notification.DefaultContinuumNotificationDispatcher.sendNotification(DefaultContinuumNotificationDispatcher.java:149)
at org.apache.maven.continuum.notification.DefaultContinuumNotificationDispatcher.buildComplete(DefaultContinuumNotificationDispatcher.java:97)
at org.apache.maven.continuum.buildcontroller.DefaultBuildController.endBuild(DefaultBuildController.java:230)
at org.apache.maven.continuum.buildcontroller.DefaultBuildController.build(DefaultBuildController.java:187)
at org.apache.maven.continuum.buildcontroller.BuildProjectTaskExecutor.executeTask(BuildProjectTaskExecutor.java:48)
at org.apache.continuum.taskqueueexecutor.ParallelBuildsThreadedTaskQueueExecutor$ExecutorRunnable$1.run(ParallelBuildsThreadedTaskQueueExecutor.java:120)
at edu.emory.mathcs.backport.java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:442)
at edu.emory.mathcs.backport.java.util.concurrent.FutureTask.run(FutureTask.java:176)
at edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:987)
at edu.emory.mathcs.backport.java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:528)
at java.lang.Thread.run(Thread.java:662)
Caused by: org.apache.maven.continuum.installation.InstallationException: cli to get mvn version return code 1
at org.apache.continuum.installation.DefaultInstallationService.getExecutorConfiguratorVersion(DefaultInstallationService.java:440)
at org.apache.maven.continuum.notification.mail.MailContinuumNotifier.getBuilderVersion(MailContinuumNotifier.java:557)
at org.apache.maven.continuum.notification.mail.MailContinuumNotifier.buildComplete(MailContinuumNotifier.java:382)
... 14 more