Scheduled task running twice from time to time

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http://serverfault.com – A customer of mine is experiencing a very strange problem: a scheduled task is running twice from time to time, with only a few seconds between execution. The task is scheduled using the windows scheduler. It's a very basic task that connects to a local service using TCP/IP, authenticate, gives it a command and disconnect. It is nearly instantaneous (the longest part actually is the SSL handshake). It triggers an issue in the server application which I will fix but my problem is that I simply cannot find any valid reason why the task is being run twice: nobody is ever connected interactively (HowTos)