Why does vetoIfFailing crash cruise control?

I am having this weird issue with Cruise Control crashing, when I add the vetoIfFailing attribute to the buildstatus element.

<cruisecontrol>
  <project>
    <modificationset>
      <buildstatus>

This causes the entire machine to say stopped for all projects:

<buildstatus logdir="/mycruisedir/logs/myproject" vetoIfFailing="true" />

... but this works:

<b开发者_运维问答uildstatus logdir="/mycruisedir/logs/myproject" />

So what is wrong with the vetoIfFailing attribute?

vetoIfFailing attribute for the buildstatus element was only added in CruiseControl v2.8.0 release notes.

I was using an earlier version - should have checked this first.