Struts Form Problem

When accessing my JSP I get the following error:
org.apache.jasp er.JasperExcept ion: Missing message for key
button.next

Can anyone tell me what the problem is? I have tried to figure this
out but am new to building webapps and struts. Thank you for your
help.

My JSP has :
<html:form action="/ContactAction">
<html:submit property="actio n">
<bean:message key="button.nex t"/>
</html:submit>
<html:submit property="actio n">
<bean:message key="button.bac k"/>
</html:submit>
<html:submit property="actio n">
<bean:message key="button.fin ish"/>
</html:submit>
</html:form>

My FormHandler has :

public final class ContactFormHand ler extends LookupDispatchA ction{
protected Map getKeyMethodMap (){
Map map = new HashMap();
map.put("button .next", "next");
map.put("button .back", "back");
map.put("button .finish", "finish");
return map;
}


public ActionForward next(ActionMapp ing mapping,
ActionForm form,
HttpServletRequ est request,
HttpServletResp onse response)
throws IOException, ServletExceptio n {
return mapping.findFor ward("success") ;
}

public ActionForward back(ActionMapp ing mapping,
ActionForm form,
HttpServletRequ est request,
HttpServletResp onse response)
throws IOException, ServletExceptio n {
return mapping.findFor ward("success") ;
}

public ActionForward finish(ActionMa pping mapping,
ActionForm form,
HttpServletRequ est request,
HttpServletResp onse response)
throws IOException, ServletExceptio n {
return mapping.findFor ward("success") ;
}

My ApplicationReso urce.properties file contains only

button.next = Next
button.back = Back
button.finish = Finish