I believe it should look like this:
function Up_pan() {
var center = map.getCenter();
var New_center = new google.maps.LatLng(center.lat() + 1, center.lng() + 1);
map.panTo(New_center);
}
The reason for this is because you weren't specifiying the right type for panTo. Note that your code is offsetting the center in a diagonal line.