Custom field error

I have added a custom field for the Client for a PO number. The custom field show up in the Add Client form. When I add a new client, I receive the following error:

A Database Error Occurred
Error Number: 1054

Unknown column 'client_custom_po_number' in 'field list'

INSERT INTO `ip_client_custom` (`client_custom_po_number`, `client_id`) VALUES ('', 2)

Filename: C:\wamp64\www\InvoicePlane\system\database\DB_driver.php

Line Number: 331

The client is added to the database.