Why can't a user see a PO in Notifications Summary?

I have a user that has PO approval ability based on his position and is found in an approval hierarchy. POs that are submitted to him for approval do not appear in the Notifications Summary list. In fact the list is empty. I have checked his employee and user set up and I don't see anything out of the ordinary. I have logged in using the user's credentials and the same thing happens to me, but when I sign on as System Admin, go to PO Approval workflow and select "View Notifications" (or something like that - don't remember the