When you inspect your database (via phpMyAdmin), you should have three configuration_key values:

1. CHECKOUT_ONE_GUEST_BILLTO_ADDRESS_BOOK_ID
2. CHECKOUT_ONE_GUEST_SENDTO_ADDRESS_BOOK_ID
3. CHECKOUT_ONE_GUEST_CUSTOMER_ID

The CHECKOUT_ONE_GUEST_CUSTOMER_ID should be associated with the "Guest Customer"'s customers-table record and the two ADDRESS_BOOK_ID values should refer to a valid entry (associated with that Guest Customer) in the site's address_book table.