I'm using the clear workspace plugin to remove everything except the two repositories that have been cloned, however when I add excludes (or even an include) the build fails with:

Deleting project workspace... Cannot delete workspace: null

On inspecting the Jenkins log, I found the following:

24-Sep-2013 13:40:21 hudson.plugins.ws_cleanup.PreBuildCleanup preCheckout
SEVERE: null
java.io.IOException: Unable to delete /home/mozilla/eideticker-ci/jenkins-master/jobs/b2g.inari.test.master/workspace/.env/include/python2.7/ImDib.h
at hudson.Util.deleteFile(Util.java:256)
at hudson.Util.deleteRecursive(Util.java:308)
at hudson.plugins.ws_cleanup.Cleanup.invoke(Cleanup.java:102)
at hudson.FilePath.act(FilePath.java:904)
at hudson.FilePath.act(FilePath.java:877)
at hudson.plugins.ws_cleanup.PreBuildCleanup.preCheckout(PreBuildCleanup.java:94)
at jenkins.scm.SCMCheckoutStrategy.preCheckout(SCMCheckoutStrategy.java:78)
at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:578)
at hudson.model.Run.execute(Run.java:1575)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:237)

It's failing to delete a file in the Python virtual environment, which I want to remove between builds. The python2.7 directory is actually a symlink so really this should only be attempting to remove the symlink and not the actual linked file...