Have you tried executing this through the command prompt? E.G "C:\Users\Administrator\Tasks\Unmanage Task.cmd". Note that the "cmd" file name and location shown in the screenshots below will be unique based on what you named the task and who you are logged into the system as.
Image may be NSFW.
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Image may be NSFW.
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Are any errors returned? Is the object unmanaged after executing this command?
