I have looked everywhere for an answer to this with no luck, my apologies if I missed it.

I am trying to send gift certificates to customers through Admin-->Gift Certificate/Coupons-->Mail Gift Certificate, but when I click send (to one or several recipients), I get a 1062 Duplicate Entry error:

1062 Duplicate entry '0' for key 4
in:
[insert into zen_coupon_email_track (coupon_id, customer_id_sent, sent_firstname, emailed_to, date_sent) values ('51', '0', 'Admin', '[email protected]', now() )]
If you were entering information, press the BACK button in your browser and re-check the information you had entered to be sure you left no blank fields.

I am currently using V.1.3.8a, however this option has never worked for me when this was the newest version and even before we updated.

Anyone have an idea what may be wrong?

Thanks!