OK, Just a simple fix -
function setbox_handler(name, minx, miny, maxx, maxy, redraw) {
document.mapserv.imgbox.value = minx + " " + miny + " " + maxx + " " +
maxy;
document.mapserv.imgxy.value = minx + " " + miny;
toFrame();//simply call the function before submit page
document.mapserv.submit();
}