Can someone explain to me why this works:

STOR ALLT(THISFORM.INVNUMB1.VALUE) TO INV
SELECT *;
FROM transactions!factgrostete INNER JOIN transactions!factgros ;
ON Factgrostete.invnumb = Factgros.invnumb;
WHERE Factgrostete.invnumb = "&INV";
INTO CURSOR QUERY1

And this does not:

STOR ALLT(THISFORM.INVNUMB1.VALUE) TO INV
SELECT *;
FROM transactions!factgrostete INNER JOIN transactions!factgros ;
ON Factgrostete.invnumb = Factgros.invnumb;
WHERE Factgrostete.invnumb = INV;
INTO CURSOR QUERY1

Whit this one I get an Operand mismatch. The INV value is character and the invnumb field is character.