I discovered the problem.
I had not considered the fact that QScrollArea use widgets and therefore perform a QScrollArea::SetWidget (widgwet). I modified the code as follows and now works correctly.

......
........
scrollBar->setValue(0);
sa->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOn) ;
sa->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysO ff);


QWidget* container = new QWidget(this);
QVBoxLayout * Elenco1 = new QVBoxLayout(container);
sa->setWidget(container);

......
...

while(i< ITEM)
{
......
.......
lineH[i].addWidget(&data[i]);
lineH[i].addWidget(&ButInfo[i]);
lineH[i].setSizeConstraint(lineH[i].SetFixedSize);

Elenco1->addLayout(&lineH[i]);
i++;
}
......
..