How long are you leaving the task for? It is meant to report back that the device is offline after a period of time.
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A power policy task will attempt to wake up any targetted device that is offline and will wait for those devices to be contactable, this is causing the task to appear to hang. As Mark said, the task should eventually come back to life but in my experience this can take a long time and obviously in an environment where WOL doesn't work this is not ideal.
Fortunately getting around the problem is easy - go into the properties of the task and click 'target devices'. Untick 'Wake up devices'. This should cause the task to behave like any other task, failing on devices which are switched off.