Server-Side:

            if (!Page.IsPostBack)
            {
                Map1.MapBackground.BackgroundBrush = new GeoSolidBrush(GeoColor.FromHtml("#E5E3DF"));
                Map1.MapUnit = GeographyUnit.DecimalDegree;

                ContextMenu menuOnEventLayer = new ContextMenu("area", 200);
                ContextMenuItem menu2 = new ContextMenuItem("click me");
                menu2.OnClientClick = "Test";
                menuOnEventLayer.MenuItems.Add(menu2);

                Feature feature = new Feature(new RectangleShape(-10, 10, 10, -10));

                Map1.CurrentExtent = feature.GetBoundingBox() ;
                Map1.HighlightOverlay.Features.Add("multipolygon", feature);
                Map1.HighlightOverlay.ContextMenu = menuOnEventLayer;
                Map1.HighlightOverlay.Style = new FeatureOverlayStyle(GeoColor.SimpleColors.Black, GeoColor.SimpleColors.Black, 1);
            }


Client-Side:


 <script type="">
        function Test() {
            var wkt = "LINESTRING(0 0,10 10)";
            var feature = new OpenLayers.Format.WKT().read(wkt);
            var style_green = {
                strokeColor: "#00FF00",
                strokeWidth: 3,
                strokeDashstyle: "dashdot",
                pointRadius: 6,
                pointerEvents: "visiblePainted"
            };
            CurrentContextMenu.display(false);
            feature.style = style_green;
            layer.addFeatures(feature);
            layer.redraw(true);
        }

        var Layer;

        function OnMapCreated(map) {
            var b = 0;
            layer = map.layers[1];
        }
    </script>