Selection rectangle on grid

Hey,

I have a problem with  TStringgrid.
I want to selected a Row from a Stringrid in my source.
I can selected it but the rectangle does not move to the selected row !
Can anybody help me ?

canSelect := true;
Stringgrid1SelectCell(Stringrid1, aCol,aRow, canSelect);

I can use this procedure but the selection-rectangle does not appear!

Greetings