change this line:
$WA_fieldValuesStr = "".((isset($_SESSION[$WA_sessionName]))?$_SESSION[$WA_sessionName]:"") ."" . "|" . "".$eCart1->DisplayInfo("Name") ."" . "|" . "".$eCart1->DisplayInfo("ID") ."" . "|" . WA_eCDB_ConvertNumber("".$eCart1->DisplayInfo("Price") ."") . "|" . WA_eCDB_ConvertNumber("".$eCart1->DisplayInfo("Quantity") ."") . "|" . "".$_SESSION['eCartCheckoutForm_cc_type'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_firstname'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_lastname'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_email'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_phone'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_fax'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_street1'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_street2'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_city'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_state_province'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_postcode'] ."" . "|" . "US" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_firstname'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_lastname'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_email'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_phone'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_fax'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_street1'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_street2'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_city'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_state_province'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_postcode'] ."" . "|" . "US" . "|" . "date(\"m-d-y\")" . "|" . "PP";
to:
$WA_fieldValuesStr = "".((isset($_SESSION['eCart1_OrderID'))?$_SESSION['eCart1_OrderID']:"") ."" . "|" . "".$eCart1->DisplayInfo("Name") ."" . "|" . "".$eCart1->DisplayInfo("ID") ."" . "|" . WA_eCDB_ConvertNumber("".$eCart1->DisplayInfo("Price") ."") . "|" . WA_eCDB_ConvertNumber("".$eCart1->DisplayInfo("Quantity") ."") . "|" . "".$_SESSION['eCartCheckoutForm_cc_type'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_firstname'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_lastname'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_email'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_phone'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_fax'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_street1'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_street2'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_city'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_state_province'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_postcode'] ."" . "|" . "US" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_firstname'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_lastname'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_email'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_phone'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_fax'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_street1'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_street2'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_city'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_state_province'] ."" . "|" . "".$_SESSION['eCartCheckoutForm_shipping_postcode'] ."" . "|" . "US" . "|" . "date(\"m-d-y\")" . "|" . "PP";