you have included the Google Maps API multiple times on this page. This may cause unexpected errors

I get two errors when using google maps API:

1. Warning: you have included the Google Maps API multiple times on this page. This may cause unexpected errors.
2. a is null (main.js)

I don't know if there is any connection between the two, but the final result is that my page cannot load the map.

Here is my head tag:

<script type="text/javascript" src="../s/Jquery/jquery-1.6.1.min.js"></script>
<script type="text/javascript" src="../s/jquery.placeholder.min.js"></script>
<script type="text/javascript" src="../s/index.js"></script>
<script type="text/javascript" src="../s/Jquery/ui/jquery.ui.core.js"></script>
<script type="text/javascript" src="../s/Jquery/ui/jquery.ui.widget.js"></script>

<script type="text/javascript" src="../s/Jquery/ui/jquery.ui.position.js"></script>
<script type="text/javascript" src="../s/Jquery/ui/jquery.ui.autocomplete.js"></script>
<script src="../dd/markerclusterer_compiled.js" type="text/javascript"></script><script src="../dd/dealers_js.js" type="text/javascript"></script><script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=false"></script>

Here is the function which I call the google map:

function set_google_map(set_region)
{
    
        var zoom;
        var center;
        switch (set_region) {
            case "usa":
                zoom = 3;
                center = new google.maps.LatLng(37.09, -95.71);
                break;
            case "europe":
                zoom = 3;
                center = new google.maps.LatLng(48.58, 7.71);
                break;
            case "eas