alhamd says:

<script type="text/javascript" src="http://maps.googleapis.com/maps/api/js?sensor=false"></script>

Change http with https.

Refer below sample.

HTML

<script type="text/javascript" src="https://maps.googleapis.com/maps/api/js?key=API_Key"></script>
<asp:TextBox ID="txtLocation" runat="server" Text=""></asp:TextBox>
<asp:Button ID="btnSearch" runat="server" Text="Search" OnClick="FindCoordinates" />
<br />
<br />
<asp:Panel ID="pnlScripts" runat="server" Visible="false">
    <div id="dvMap" style="width: 300px; height: 300px">
    </div>
    <script type="text/javascript">
        var markers = [
        <asp:Repeater ID="rptMarkers" runat="server">
        <ItemTemplate>
                {
                    "title": '<%# Eval("Address") %>',
                    "lat": '<%# Eval("Latitude") %>',
                    "lng": '<%# Eval("Longitude") %>',
                    "description": '<%# Eval("Address") %>'
                }
        </ItemTemplate>
        <SeparatorTemplate>
            ,
        </SeparatorTemplate>
        </asp:Repeater>
        ];
    </script>
    <script type="text/javascript">
    window.onload = function () {
        var mapOptions = {
            center: new google.maps.LatLng(markers[0].lat, markers[0].lng),
            zoom: 13,
            mapTypeId: google.maps.MapTypeId.ROADMAP
        };
        var infoWindow = new google.maps.InfoWindow();
        var map = new google.maps.Map(document.getElementById("dvMap"), mapOptions);
        for (i = 0; i < markers.length; i++) {
            var data = markers[i]
            var myLatlng = new google.maps.LatLng(data.lat, data.lng);
            var marker = new google.maps.Marker({
                position: myLatlng,
                map: map,
                title: data.title
            });
            (function (marker, data) {
                google.maps.event.addListener(marker, "click", function (e) {
                    infoWindow.setContent(data.description);
                    infoWindow.open(map, marker);
                });
            })(marker, data);
        }
    }
    </script>
</asp:Panel>

Namespaces

C#

using System.Data;
using System.IO;
using System.Net;
using System.Text;

VB.Net

Imports System.Data
Imports System.IO
Imports System.Net
Imports System.Text

Code

C#

protected void FindCoordinates(object sender, EventArgs e)
{
    string url = "https://maps.google.com/maps/api/geocode/xml?address=" + txtLocation.Text + "&key=API_Key";
    WebRequest request = WebRequest.Create(url);
    using (WebResponse response = (HttpWebResponse)request.GetResponse())
    {
        using (StreamReader reader = new StreamReader(response.GetResponseStream(), Encoding.UTF8))
        {
            DataSet dsResult = new DataSet();
            dsResult.ReadXml(reader);
            DataTable dtCoordinates = new DataTable();
            dtCoordinates.Columns.AddRange(new DataColumn[4] { new DataColumn("Id", typeof(int)),
                new DataColumn("Address", typeof(string)),
                new DataColumn("Latitude",typeof(string)),
                new DataColumn("Longitude",typeof(string)) });
            foreach (DataRow row in dsResult.Tables["result"].Rows)
            {
                string geometry_id = dsResult.Tables["geometry"].Select("result_id = " + row["result_id"].ToString())[0]["geometry_id"].ToString();
                DataRow location = dsResult.Tables["location"].Select("geometry_id = " + geometry_id)[0];
                dtCoordinates.Rows.Add(row["result_id"], row["formatted_address"], location["lat"], location["lng"]);
            }
            if (dtCoordinates.Rows.Count > 0)
            {
                pnlScripts.Visible = true;
                rptMarkers.DataSource = dtCoordinates;
                rptMarkers.DataBind();
            }
        }
    }
}

VB.Net

Protected Sub FindCoordinates(ByVal sender As Object, ByVal e As EventArgs)
    Dim url As String = "https://maps.google.com/maps/api/geocode/xml?address=" & txtLocation.Text & "&key=API_Key"
    Dim request As WebRequest = WebRequest.Create(url)
    Using response As WebResponse = CType(request.GetResponse(), HttpWebResponse)
        Using reader As StreamReader = New StreamReader(response.GetResponseStream(), Encoding.UTF8)
            Dim dsResult As DataSet = New DataSet()
            dsResult.ReadXml(reader)
            Dim dtCoordinates As DataTable = New DataTable()
            dtCoordinates.Columns.AddRange(New DataColumn(3) {
                                            New DataColumn("Id", GetType(Integer)),
                                            New DataColumn("Address", GetType(String)),
                                            New DataColumn("Latitude", GetType(String)),
                                            New DataColumn("Longitude", GetType(String))})
            For Each row As DataRow In dsResult.Tables("result").Rows
                Dim geometry_id As String = dsResult.Tables("geometry").[Select]("result_id = " & row("result_id").ToString())(0)("geometry_id").ToString()
                Dim location As DataRow = dsResult.Tables("location").[Select]("geometry_id = " & geometry_id)(0)
                dtCoordinates.Rows.Add(row("result_id"), row("formatted_address"), location("lat"), location("lng"))
            Next
            If dtCoordinates.Rows.Count > 0 Then
                pnlScripts.Visible = True
                rptMarkers.DataSource = dtCoordinates
                rptMarkers.DataBind()
            End If
        End Using
    End Using
End Sub

Screenshot