I am getting error message #: 1886 "Index does not accept null". I am using free tables. I am getting this error on the "SQL Select Statement Listed Below.:

*************************************************************************
PARAMETERS tdExpiry, tcReturnMsg, tlUserInterface, tnSize, tcMaker,; tcVacc, tcLot, tnStockID, tdOthrExp, tnOthSize

lcErrorWarning = "Q"

**************************************************
** Conditions for Size and Expiry Datwe change **
**************************************************
SELECT Expiry, Size, lot FROM Stock WHERE Maker == tcMaker ;
AND Vaccine == tcVacc AND !DELETED() AND ;
Lot == OLDVAL("Lot","Stock") AND (Stock.StockID <> tnStockID OR OLDVAL ;("Size","Stock") != tnSize OR ;
OLDVAL("Expiry","Stock") != tdExpiry OR OLDVAL("Lot","Stock") != tcLot ) ;
INTO CURSOR TStock
***************************************************************************

Please advise me on what is wrong with this statement and how can I correct it.




Thank You In Advance



Winfred Majors