This Knowledgebase article provides details about the error message below:
[U25]Operation Stop Replication on Passive failed - continuing.
Message in the NFLog:
[ControllerStop](com.neverfail.controller.Pair) - [U25]Operation Stop Replication on Passive failed - continuing.
java.lang.IllegalStateException: Timer already cancelled.
Immediately prior to this exception, a java.lang.OutOfMemoryError can be found. This last exception causes the java Timer class to set its newTasksMayBeScheduled to false - which makes it throw an IllegalStateException the next time we try to do a schedule. In other words, being out of memory, the Controller can not schedule the TimerTask, nor can it allocate a new one and try to schedule it.
Starting with version 5.2, the Controller has a code fix so that if this specific error occurs it will ignore the exception and continue on with the close.