For any body who is reading this page, this might help...
I faced the same problem only for the first time i start the application, it was tricky and i found that in the web.xml, i did not load the ActionServlet during the start-up and it had not parsed the struts-config.xml when the request had come. The problem is solved when i added the following line in web.xml ActionServlet's configuration,
<load-on-startup>1</load-on-startup>