Cannot find message resources under key org.apache.struts.action.MESSAGE

I am I newbie learning struts, the following error is haunting me. Can anybody please provide the solution, or tell me the probable causes for such an error.

Details.
 I have the ApplicationResources(resourcebundle) files in the

C:\Tomcat\webapps\bookex\WEB-INF\classes
directory

Cannot find message resources under key org.apache.struts.action.MESSAGE

I have the following files:

c:\Tomcat\webapps\bookex\index.jsp



<%@ taglib uri="/WEB-INF/struts-tiles.tld" prefix="tiles" %>

<tiles:insert page="/siteLayout.jsp" flush="true">
    <tiles:put name="title" type="string"
                     value="Get Wrox Stock Quote" />
    <tiles:put name="header" value="/header.jsp" />
    <tiles:put name="footer" value="/footer.jsp" />
    <tiles:put name="content" value="/indexContent.jsp"/>
</tiles:insert>


Looking forward for a response.