Receiving Problem

I have a user at one of our plants that is trying to do Goods Receiving. 
When he enters the information, he gets the message "Deliveries are not 
due yet".  This happens on the blanket po's.  Seems to me they would just 
need to change a date somewhere so they could receive against the po's, 
but I'm not sure where or how as this is not something I do.  Can someone 
help?

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