ASPX Code:

    <script id="MapUpdateCode" type="text/javascript">
        var olMap = null;http://gis.thinkgeo.com/DesktopModules/ActiveForums/themes/thinkgeo/save32.png
        var markers = null;
        sRptType = window.location.search.substring(1);
        
        var OnMapCreating = function(map) {
            if (Map1 != null)
            {
                markers = new OpenLayers.Layer.Markers("Markers");
                Map1.GetOpenLayersMap().addLayer(markers);
            }
        };

        var OnMapCreated = function(map) {
 
            if (sRptType == 'GPS')
            {
                var timer = window.setInterval(Function.createDelegate({ 'args': "args", 'context': document.getElementById('message') }, function(evt) {
                var args = this.args;
                var context = this.context;
                <%=ClientScript.GetCallbackEventReference(Me, "args", "Success", "context", "Error", true) %>;
                }), <%= Session("TimerInterval") %>);
            }
            else
            {
                ShowibtnTracking(false);
            }
        };
        
        function SelectedUnitChanged(el) {
            //var txt = document.getElementsByName("Label4");
            //txt.value = el.options[el.selectedIndex].text;
            //document.getElementById("Label4").innerText = txt.value;
            ShowpnTracking(true);
        }
        
        function Success(args, context) 
        {
            
            if (context != null)
            {
                var vehicles = Sys.Serialization.JavaScriptSerializer.deserialize(args);
                if (markers != null)
                {
                    if (markers.markers != null) 
                    {
                        while (markers.markers.length > 0) 
                        {
                            markers.markers[0].destroy();
                            markers.removeMarker(markers.markers[0]);
                        }
                    }
                
                    olMap = Map1.GetOpenLayersMap();
                    if (olMap.popups != null) 
                    {
                        while (olMap.popups.length > 0) 
                        {
                            olMap.popups[0].destroy();
                        }
                    }
                    for(var i = 0; i<vehicles.length; i++)
                    {
                        var vehicle = vehicles[i];
                        var size = new OpenLayers.Size(32, 32);
                        var offset = new OpenLayers.Pixel(-(size.w / 2), -size.h);
                        //var icon = new OpenLayers.Icon('../../theme/' + vehicle.n, size, offset);
                        var icon = new OpenLayers.Icon('./theme/default/img/marker_blue.gif', size, offset);
                 
                        var marker = new OpenLayers.Marker(new OpenLayers.LonLat(vehicle.x, vehicle.y), icon);
                        markers.addMarker(marker);
                        AddPopup(marker, vehicle.id, vehicle.spd, vehicle.Direction, vehicle.DT, vehicle.Address, vehicle.y, vehicle.x, vehicle.Opr8r, "siteDesc", "DisplayText");
                    }
                }    
                            }
        }

        function Error(args, context) {
            message.innerText = 'EXCEPTION';
        }
        
        function AddPopup(marker, siteId, spd, Direction, DT, Address, lat, lon, Opr8r, siteDesc, DisplayText) {
            var tmp_X = 0;
            var tmp_Y = 0;

            var content = "<span class='popup'>\r\n"
            
            if (Opr8r == "None")
            {
                content = content + "<div>" + siteId + "</div>\r\n"
            }
            else
            {
                content = content + "<div>" + siteId + " (" + Opr8r + ")</div>\r\n"
            }
            
            content = content + "<div>" + DT + "</div>\r\n"
            content = content + "<div>Direction: " + Direction + " deg</div>\r\n"
            content = content + "<div>Speed: " + spd + " " + "</div>\r\n"
            content = content + "<div>" + Address + "</div>\r\n"
           
            //content = content + "<div>" + lat + "</div>\r\n"
            //content = content + "<div>" + lon + "</div>\r\n"

            content = content + "</span>"

            var popup = new OpenLayers.Popup.FramedCloud(siteId,
                   new OpenLayers.LonLat(parseFloat(lon), parseFloat(lat)),
                   new OpenLayers.Size(200, 200),
                   content,
                   null,
                   true);

            olMap = Map1.GetOpenLayersMap();
            olMap.addPopup(popup);
            //popup.hide();

//            for (i in olMap.popups) {
//                if (olMap.popups[i].visible && olMap.popups[i] != popup) {
//                    olMap.popups[i].hide();
//                }
//            }

//            marker.events.register('mouseover', popup, function(evt) {
//                popup.show();
//            });

//            marker.events.register('mouseout', popup, function(evt) {
//                for (i in olMap.popups) {
//                    if (olMap.popups[i].visible) {
//                        olMap.popups[i].hide();
//                    }
//                }
//            });
        }
    </script>
    
    
    Code Behind:
    
    Private Shared result As String = String.Empty
    Private vehicles As New Collection(Of JsonVehicle)()
    Private Shared iRecordPos As Integer = 0
    Private Shared iRecordCount As Integer = 0


    Public Sub RaiseCallbackEvent(ByVal eventArgument As String) Implements System.Web.UI.ICallbackEventHandler.RaiseCallbackEvent

        '+--------------------------------------------------------------+
        '|  This sub contains call back code executed from the client   |
        '|  side when the javascript timer fires.                       |
        '+--------------------------------------------------------------+

        '**
        '** If we're executing a data archive report, don't execute code here.
        '**
        If Session("ReportType") = "DATA" Then
            Exit Sub
        End If

        '** 
        '** The following construct allows for the display of different GPS positions
        '** from the dataset stored in memory for the selected unit.  This is accomplished
        '** via a combination of client-side script, server-side data handling, and session
        '** variables to store everything.
        '**
        Dim OriginalLon As Double = 0
        Dim OriginalLat As Double = 0
        Dim spd As Double = 0
        Dim DT As DateTime
        Dim Direction As Integer
        Dim projectedLat As Double = 0
        Dim projectedLon As Double = 0
        Dim Address As String = ""
        Dim Opr8r As String = ""

        vehicles.Clear()
        iRecordPos = Session("iRecordPos")

        If Session("dv").Table.Rows.Count > 0 Then

            lon = Session("dv").item(iRecordPos).item("Lon")
            lat = Session("dv").item(iRecordPos).item("Lat")

            OriginalLon = lon
            OriginalLat = lat

            If hidPlaybackMode.Value = "Stopped" Then
                iRecordPos = 0
                Session("iRecordPos") = 0
                lon = Session("dv").item(iRecordPos).item("Lon")
                lat = Session("dv").item(iRecordPos).item("Lat")
                spd = Session("dv").item(iRecordPos).item("Knots") '* sngSpeedMultiplier
                Direction = Session("dv").item(iRecordPos).item("Direction")
                DT = Format(Session("dv").item(iRecordPos).item("Date_Time"), "dd-MM-yyyy hh:mm:ss")
                Address = Session("dv").item(iRecordPos).item("Address")
                Opr8r = Session("dv").item(iRecordPos).item("Unit_Operator")

                ProjectVehicles2(lon, lat)
                Dim vehicle As New JsonVehicle(cboUnitSelection.Text, "marker_blue.gif", spd, Direction, DT, Address, lon, lat, Opr8r)
                vehicles.Add(vehicle)
            End If

            If hidPlaybackMode.Value = "Playing" Or hidPlaybackMode.Value = "Paused" Then
                '** User is playing
                If Not iRecordPos = Session("dv").count - 1 Then
                    iRecordPos = Session("iRecordPos")
                    lon = Session("dv").item(iRecordPos).item("Lon")
                    lat = Session("dv").item(iRecordPos).item("Lat")
                    spd = Session("dv").item(iRecordPos).item("Knots") '* sngSpeedMultiplier
                    Direction = Session("dv").item(iRecordPos).item("Direction")
                    DT = Format(Session("dv").item(iRecordPos).item("Date_Time"), "dd-MM-yyyy hh:mm:ss")
                    Address = Session("dv").item(iRecordPos).item("Address")
                    Opr8r = Session("dv").item(iRecordPos).item("Unit_Operator")

                    Select Case rbtnlstSpeedUnits.SelectedValue
                        Case "Slow"
                            Session("TimerInterval") = 2000
                        Case "Medium"
                            Session("TimerInterval") = 1000
                        Case "Fast"
                            Session("TimerInterval") = 500
                    End Select


                    ProjectVehicles2(lon, lat)

                    Dim vehicle As New JsonVehicle(cboUnitSelection.Text, "marker_blue.gif", spd, Direction, DT, Address, lon, lat, Opr8r)
                    vehicles.Add(vehicle)

                    If hidPlaybackMode.Value = "Playing" Then
                        iRecordPos += 1
                        Session("iRecordPos") += 1
                    End If

                End If

                Session("cb_RecordPos") = iRecordPos & " of " & Session("dv").Count - 1

                If iRecordPos = Session("dv").Count - 1 Then
                    hidPlaybackMode.Value = "Stopped"
                    iRecordPos = 0
                    Session("iRecordPos") = 0
                    lon = Session("dv").item(iRecordPos).item("Lon")
                    lat = Session("dv").item(iRecordPos).item("Lat")
                    spd = Session("dv").item(iRecordPos).item("Knots") ' * sngSpeedMultiplier
                    Direction = Session("dv").item(iRecordPos).item("Direction")
                    DT = Format(Session("dv").item(iRecordPos).item("Date_Time"), "dd-MM-yyyy hh:mm:ss")
                    Address = Session("dv").item(iRecordPos).item("Address")
                    Opr8r = Session("dv").item(iRecordPos).item("Unit_Operator")

                    ProjectVehicles2(lon, lat)
                    Dim vehicle As New JsonVehicle(cboUnitSelection.Text, "marker_blue.gif", spd, Direction, DT, Address, lon, lat, Opr8r)
                    vehicles.Add(vehicle)
                End If

            End If

            If hidPlaybackMode.Value = "Previous" Or hidPlaybackMode.Value = "Next" Then
                '** User is playing
                If Not iRecordPos = Session("dv").count - 1 Then
                    iRecordPos = Session("iRecordPos")
                    lon = Session("dv").item(iRecordPos).item("Lon")
                    lat = Session("dv").item(iRecordPos).item("Lat")
                    spd = Session("dv").item(iRecordPos).item("Knots") '* sngSpeedMultiplier
                    Direction = Session("dv").item(iRecordPos).item("Direction")
                    DT = Format(Session("dv").item(iRecordPos).item("Date_Time"), "dd-MM-yyyy hh:mm:ss")
                    Address = Session("dv").item(iRecordPos).item("Address")
                    Opr8r = Session("dv").item(iRecordPos).item("Unit_Operator")

                    ProjectVehicles2(lon, lat)

                    Dim vehicle As New JsonVehicle(cboUnitSelection.Text, "marker_blue.gif", spd, Direction, DT, Address, lon, lat, Opr8r)
                    vehicles.Add(vehicle)

                    If hidPlaybackMode.Value = "Next" Then
                        iRecordPos += 2
                        Session("iRecordPos") += 2
                        hidPlaybackMode.Value = "Paused"
                    End If

                    If hidPlaybackMode.Value = "Previous" Then
                        iRecordPos -= 2
                        Session("iRecordPos") -= 2
                        hidPlaybackMode.Value = "Paused"
                    End If

                End If
            End If

            'For i As Integer = 0 To startPositions.GetLength(0) - 1
            '    Dim lon As Double = startPositions(i, 0) + New Random().[Next](-12, 20) / 5000.0R
            '    Dim lat As Double = startPositions(i, 1) + New Random().[Next](-11, 26) / 5000.0R

            '    If DirectCast(Session("MapTypeObj"), MapType).MapProvider <> MapProvider.WorldMapKit Then
            '        projectedLat = lat
            '        projectedLon = lon
            '        ProjectVehicles2(projectedLon, projectedLat)
            '    Else
            '        projectedLat = lat
            '        projectedLon = lon
            '    End If

            '    startPositions(i, 0) = lon
            '    startPositions(i, 1) = lat
            '    'Dim vehicle As New JsonVehicle("vehicle" & (i + 1), "vehicle_van_" & (i + 1) & ".png", projectedLon, projectedLat)
            '    'vehicles.Add(vehicle)
            'Next

            result = JsonSerializeHelper.Serialize(Of Collection(Of JsonVehicle))(vehicles)
        End If

    End Sub

    Public Function GetCallbackResult() As String Implements System.Web.UI.ICallbackEventHandler.GetCallbackResult
        'Return the vehicle data to client using callback
        Return result
    End Function
    
    ''' <summary>
    ''' This sub allows us to project vehicles using decimal degrees into other units such as meters
    ''' which is used by all of the online web mapping services.
    ''' </summary>
    ''' <param name="Lon"></param>
    ''' <param name="Lat"></param>
    ''' <remarks></remarks>
    Private Sub ProjectVehicles2(ByRef Lon As Double, ByRef Lat As Double)

        If DirectCast(Session("MapTypeObj"), MapType).MapProvider <> MapProvider.WorldMapKit Then

            '**
            '** Keep remmed out code for when a switch for multiple vehicle display is implemented.
            '**
            Dim proj4 As New Proj4Projection(Proj4Projection.GetEpsgParametersString(4326), Proj4Projection.GetGoogleMapParametersString())

            proj4.Open()

            'For Each item As KeyValuePair(Of String, Vehicle) In vehicles
            Dim vertex As Vertex = proj4.ConvertToExternalProjection(Lon, Lat)
            'item.Value.X = vertex.X
            'item.Value.Y = vertex.Y
            'Next

            Lon = vertex.X
            Lat = vertex.Y
            proj4.Close()

        End If

    End Sub