In order to delete a client, all invoices must be paid, and all paid transactions need to be cleared.  This is hard to do accidentally.  Did you actually go through the two or three individual steps I just indicated?

Is it possible that you have just by accident changed the name of the customer and then saved the customer record again?  I can't tell you how many customers I've seen in books with z or . as a customer name.  Or is it possible you inactivated them and therefore are not showing up everywhere right now?

Run the Customer/Client List report from the Reports menu and make sure you include Inactive clients.  Then look through it for the client's address or other info you recall.

Oh thank you. I will try this right away! 

Hi Michelle Brunet  if this suggested answer helped, please mark it as verified  (by clicking the "Verify Answer" button next to Reply, on the response) for the benefit of others in this forum . Thank you!

This did indeed work!

Glad it worked and you found the entry.  The alternate option was to do a data repair to reinsert the customer information but the customer history would already be gone at that point and if the lookup information is still there, it might have to be reattached to the customer.