Included Workers not qualified to take study

Sometimes MTurk takes a few minutes (or longer) for the Qualification to propagate through their system. (That is why you can't click on email included workers for a few  minutes until that is complete)

Also, there may be additional qualifications like 90% approval rating which might disqualify them.
Finally, they may have completed or accepted and then returned the study in which case they are also invalidated.  

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