"There is a task currently being executed. Please, wait until the task is finished, before starting a new task."the culprit is usually that a download or change has stalled and sophos is unable to honor the request. unfortunately, there is not a corresponding error message in the sophos or system event log.
to right sophos, do the following, per sophos technical support:
"Close down the consoles on your server, the open your Task Manager and click on Processes. On that list kill the DLLLOADER.EXE process. Next go into services and restart the 'Sophos Enterprise Manager Scheduler service.' Now go into EmLibrary and change your parent and it should take this time."