Google maps -- a is undefined

Hi there,
I solve all day long a problem with error "a is undefined".
I have 2 pages -- index and the second page. On the second page I shows google map in div and all is alright.
But on index page I get error message given in subject this thread (on index page is not div with google map).

I am including this code to my page:

<script type="text/javascript" src="http://maps.google.com/maps?
file=api&amp;v=2&amp;key=my_key"></script>

<script>
$(function(){
      function createMarker(point){
         var marker = new GMarker(point, {draggable: true});
          GEvent.addListener(marker,"mouseup",function(){
          $("#location").val(marker.getPoint().lat());

          $("#frmfirstForm-gmap_lat").val(marker.getPoint().lat());
          $("#frmfirstForm-gmap_lng").val(marker.getPoint().lng());
         });
         return marker;
      }

      function setLocation(zip){
        var geocoder = new GClientGeocoder();
        geocoder.setBaseCountryCode('cz');
        geocoder.getLocations(zip, function(locations){
          if(locations.Status.code === 200){
            // toSource not for IE!!!
            var p = locations.Placemark[0].Point;
            //setup globaly vars for show image-map in summary page
            lat = p.coordinates[1];
              lng = p.coordinates[0];

            var loc = new GLatLng(p.coordinates[1],
p.coordinates[0]);
            map.addOverlay(createMarker(loc));
            map.setCenter(loc);
          }
        });
      }

      var map = new GMap2($("#gmap").get(0));
      map.addControl(new GLargeMapControl());
      var loc_lat = 49.3268;
      var loc_lng = 17.9966;
      var location = new GLatLng(loc_lat, loc_lng);

      $("#frmfirstForm-gmap_lat").val(loc_lat);
      $("#frmfirstForm-gmap_lng").val(loc_lng);

    });
</script>

Can you help me, please, how this error message remove?

Thank you very much.