Gary,
This can be done from the Task itself. Go to the Task and then maximize the Resource Panel which will show you all of the resources. Click on the Gear Icon and select Manage. Add the <Resource>.State field. This shows you the State of the Resource on the task (not the Resource State which is different). You should see the user's Resource.State with a blue lock icon, double click on it to change the user from Inactive to Active (will show green play icon).
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