Is it possible to delete Expiration Date in the Credit Card form ?

An Expiration Date was inadvertantly entered in the Credit Card form (Payables Manager > Credit Cards > Credit Cards) for one specific employee (these are actually P-cards).  When the expiration date is deleted and click Save, the message in lower left is "No changes to save".  When same card is re-queried, expiration date is still there.  Is there another form that controls the expiration date ?  Is it possible to delete an expiration date ?  In this case, expiration date is a future date 12/31/2019. 

Thanks for any insight.

David