Can people help on how to change this query to run in VFP9 from VFP7?

Group by is invalid is the error

SELECT Invhead.orderid, Invhead.invoiceno, Invhead.invoicedate,;
Customer.Code as Code, Invhead.freight, Invhead.brokerage, ;
Ordhead.entered, Customer.name AS custname, Ordhead.location, ;
Invprod.invoiceqty, SUM(invoiceqty*sellprice) as Value, ;
SUM(invprod.invoiceqty*ordprod.sellprice)*(InvHead.Discount/100) as Discount, ;
(SUM(invprod.invoiceqty*ordprod.sellprice)-(SUM(invprod.invoiceqty*ordprod.sellprice)*(InvHead.Discount/100)) + InvHead.Freight)*(InvHead.Tax/100) as Tax ;
FROM invhead, invprod, ordhead, ordprod, customer ;
WHERE Invhead.orderid = Ordhead.orderid ;
AND Invhead.invoiceno = Invprod.invoiceno ;
AND Ordhead.customerid = Customer.customerid ;
AND Ordhead.orderid = Ordprod.orderid ;
AND Invprod.productid = Ordprod.productid ;
GROUP BY Invhead.invoiceno ;
INTO CURSOR salejour


Needless to say, adding all fields to the group by gives more records...

Help!

TIA,
Mike