If you edited a guest customer in the admin area and this customer's email address already exists in another customer record, you cannot successfully save the guest customer until you change the email address to something unique.

Small change to the query on line 143 of /admin/customers.php fixes this problem:

//guest account
$check_email = tep_db_query("select customers_email_address from " . TABLE_CUSTOMERS . " where customers_email_address = '" . tep_db_input($customers_email_address) . "' and customers_id != '" . (int)$customers_id . "' AND guest_flag!=1");

. not full package
. only corrected file

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