string applicationPath = Page.Request.ApplicationPath;

if (!Page.Request.ApplicationPath.EndsWith("/"))

  {

     applicationPath = string.Format("{0}{1}", Page.Request.ApplicationPath, "/");

  }

string helpUrl = string.Format("{0}{1}", Page.Request.Url.Scheme + "://" + Page.Request.Url.Authority + applicationPath, "Help/GlobalSearch.htm");