issue regarding SiteMap.Provider.FindSiteMapNodeFromKey in asp.net webform project

Question

i am working with asp.net 4.0 webform project. when i am accessing a then site map title is not showing for that page.

here is my site map file detail

<?xml version="1.0" encoding="utf-8" ?>
<siteMap xmlns="http://schemas.microsoft.com/AspNet/SiteMap-File-1.0" >
<siteMapNode url="~/index.aspx" title="Home"  description="The WebSite's Home Page">
<siteMapNode url="~/UPS/UPSLabelFormUK.aspx" title="UK Label"  description="UK Label" />
<siteMapNode url="~/ContactUS.aspx" title="ContactUS"  description="Contact US" />
<siteMapNode url="~/KnowledgeBase.aspx" title="Knowledge Base"  description="KnowledgeBase" />
<siteMapNode url="~/PartBase.aspx" title="PartSearch"  description="Part Search" />  
</siteMapNode>
</siteMap>

i am accessing UPSLabelFormUK.aspx like localhost:4990/UK/Label then some time title is displaying on the page and sometime not. page is coming because i wrote routing code for that like

 void Application_Start(object sender, EventArgs e)
  {

    RouteTable.Routes.MapPageRoute("UK_Label", "UK/Label", "~/UPS/UPSLabelFormUK.aspx");
    SiteMap.SiteMapResolve += SiteMap_SiteMapResolve;
  }

i debug the code and found that sometime node is being null. here is the line in SiteMapResolve event

node = SiteMap.Provider.FindSiteMapNode(handler.VirtualPath);

my partial code in sitemap resolve event look like

var node = SiteMap.CurrentNode;
    var rc = HttpContext.Current.Request.RequestContext;
    if (rc.HttpContext != null)
    {
      try
      {
        var route = rc.RouteData.Route;
        if (route != null)
        {
          // when node found in sitemap file and url is routing url
          var page = HttpContext.Current.CurrentHandler as System.Web.UI.Page;
          //var segments = route.GetVirtualPath(rc, null).VirtualPath.Split('/');
          //var path = "~/" + string.Join("/", segments.Take(segments.Length - rc.RouteData.Values.Count).ToArray());
          //node = SiteMap.Provider.FindSiteMapNodeFromKey(path);

          if (page != null && page.RouteData != null)
          {
            // if the current page wasn't found in the sitemap, maybe it was becase of routing... let's find out
            if (node == null)
            {
              // See if this page has a route
              var handler = page.RouteData.RouteHandler as PageRouteHandler;
              // if it was a page Route handler, we are in business
              if (handler != null)
              {
                // try and find the virutal path of the .aspx actually handling the request instead.
                node = SiteMap.Provider.FindSiteMapNode(handler.VirtualPath);
              }
            }
          }

can anyone tell me why node is getting null when virtual path return ~/UPS/UPSLabelFormUK.aspx and this url exist in my sitemap file. please suggest me the right solution.