Diagnosis
You have not specified a PO Box postal code for a PO Box address,although the 'PO Box postal code required' flag is set for the currentcountry. You can activate/deactivate this flag in the country-specificcheck customizing in the general settings.

Procedure
If the 'PO Box postal code required' flag is set, you must maintain thePO Box postal code if a PO Box is specified (or the 'No PO Box number'flag is set).