impossible to use Set in a onLoad function with flash 8

One could explain why this script works well with flash MX but not with Flash
8?
Thre trace command give me "bague" as expected with flash MX but "undefined"
with Flash 8 !!? :confused;

=====================================
tout= new LoadVars();


tout.onLoad = function () {
for (i in tout){ set(i,tout); }

trace (produit);
}

tout.load("vars.txt");
=====================================
vars.txt contains : produit="bague"&produit2="bracelet"