Google map is not loaded after partial postback

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ASP.NET

Ajax

Google-Maps

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I have a Google Map on which I display markers by fetching the latlng's from a database on a Button Click. To avoid postback I put this button in an update panel.

<asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
        <ContentTemplate>
        <asp:Button ID="Button1" runat="server" onclick="Button1_Click" 
            style="z-index: 1; left: 778px; top: 270px; position: absolute; height: 25px" Text="Button" />
        </ContentTemplate>
        <Triggers>
        <asp:AsyncPostBackTrigger ControlID="Button1" EventName="Click" />
        </Triggers>
    </asp:UpdatePanel>

Button_Click:

protected void Button1_Click(object sender, EventArgs e)
    {
        //Some code to fetch latlng's from database
        //Passing the final needed value to a <asp:HiddenField> at this point
        ScriptManager.RegisterClientScriptBlock(this, typeof(Button), "currentloc", "showcurrent()", true);
    }

Javascript in aspx:

function showcurrent()
    {
     var rec_loc= document.getElementById('<%=currentloc.ClientID %>').value;
     var splitloc=[];
     splitloc= rec_loc.split(',');
     var clat=parseFloat(splitloc[0]);
     var clng=parseFloat(splitloc[1]);
     var cpos= new google.maps.LatLng(clat,clng);
     var cmarker= new google.maps.Marker({icon:'http://www.googlemapsmarkers.com/v1/A/0099FF/', position:cpos,map:map});  
     map.setCenter(cmarker.getPosition());
    }

In body onload I initialize and load the map and its fine. But when I click the button, I end up with a blue screen in the map(the map controls like zoom, etc are still there though). Where am I doing wrong? Please help.