ZC 1.3.9h, upgrade from 1.3.9a via officially sanctioned route
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We recently had a customer place an order via credit card. The order went through fine, except that in the admin end, there was no customer information.

After some poking around, I looked in the customer database and discovered a 0 value in the field customers_default_address_id.

I'm guessing this is probably the issue, since all the other customers had some kind of value in that field.

We've tried to delete the customer record via the ZC admin interface, but it won't let us.

So....

1) What might have caused this?
2) How can we delete the customer so they can reenter their information?

Thanks,

John