cruisecontrol.net build number doesn't increment

We use Cruise Control .Net as our build server. For our version numbering we use SvnRevionLabeller with the following config

<labeller type="svnRevisionLabeller">
        <major>0</major>
        <minor>1</minor>
        <versionFile>VersionInfo.cs</versionFile>
        <url>$(svn_src)/project/trunk</url>
开发者_如何学C        <executable>$(svn_exe)</executable>
        <username>$(svn_user)</username>
        <password>$(svn_password)</password>
        <incrementOnForce>true</incrementOnForce>
</labeller>

This works fine except after a broken build. The build number generated is the same as the build number of the last correct build before the broken ones. What setting do we need to give the new correct build an incremented build number?