This can't be good.

Got this on hudson 1.242

SEVERE: Executor throw an exception unexpectedly
java.lang.IllegalMonitorStateException
at java.util.concurrent.locks.ReentrantLock$Sync.tryRelease(ReentrantLock.java:127)
at
java.util.concurrent.locks.AbstractQueuedSynchronizer.release(AbstractQueuedSynchronizer.java:1140)
at java.util.concurrent.locks.ReentrantLock.unlock(ReentrantLock.java:431)
at hudson.model.Build.onEndBuilding(Build.java:74)
at hudson.model.Run.run(Run.java:849)
at hudson.model.Build.run(Build.java:84)
at hudson.model.ResourceController.execute(ResourceController.java:70)
at hudson.model.Executor.run(Executor.java:88)