I have a map in which I apply a custom overlay using KMbox overlay to signify where I think the users general point of interest lies. What I want is to display this map to the user and allow them to click on the map to give me an exact location match of their POI.

This all works fine except for when the user clicks on the map and changes the zoom of the map.

Here's my code to add the marker to the map.

 function addMarker(location) {

        if(KmOverlay)
        {
            KmOverlay.remove();
        }
        if(last_marker)
        {
            last_marker.setMap(null);
        }

        marker = new google.maps.Marker({
            position: location,
            map: map
        });

        // Keep track for future unsetting...
       last_marker = marker;     
    }

And to show the map I have this function.

function show_map(lt, ln, zoom, controls, marker) 
{
    var ltln = new google.maps.LatLng(lt, ln);
    var vars = {
        zoom: zoom,
        center: ltln,
        mapTypeId: google.maps.MapTypeId.ROADMAP,
        navigationControl: controls,
        navigationControlOptions: {style: google.maps.NavigationControlStyle.ZOOM_PAN} ,
        mapTypeControl: false,
        scaleControl: false,
        scrollwheel: false
    };

    map = new google.maps.Map(document.getElementById("map_canvas"), vars);

    KmOverlay = new KmBox(map, new google.maps.LatLng(lat, lon), KmOpts);
    var totalBounds = new google.maps.LatLngBounds();
    totalBounds.union(KmOverlay.getBounds());


    google.maps.event.addListener(map, 'click', function(event) {
        addMarker(event.latLng);
    });

}

I have a working example at the following link here