This is a fraud security feature of the AARP cards when being applied. It is best to enter 5 at a time. It is a lock out feature, which is a way to keep someone entering multiple cards, possibly fraudulent. So, enter more cards an hour or so later. My TA does this for me.
AARP always says, call PCL, they will help. No, they have no clue. I told AARP that they had to fix it. I called the rewards number and them spoke to a supervisor at Customer care. They got back to me the next day and reinstated the GC that showed 0 balance.
Now, before I use them, I check the balance on each one, before I use it with my TA or also before I use one of them OB for OBC.