FacesMessage a4j:commandButton prevents from displaying a:errors - jsf

Question

I have the following jsp page that has the following lib imports:
<%# taglib uri="http://java.sun.com/jsf/html" prefix="h"%>
<%# taglib uri="http://java.sun.com/jsf/core" prefix="f"%>
<%# taglib uri="/WEB-INF/alfresco.tld" prefix="a"%>
<%# taglib uri="http://myfaces.apache.org/tomahawk" prefix="t"%>
<%# taglib uri="http://richfaces.org/a4j" prefix="a4j"%>
<%# taglib uri="http://richfaces.org/rich" prefix="rich"%>
<%# page buffer="32kb" contentType="text/html;charset=UTF-8"%>
<%# page isELIgnored="false"%>
<%# page import="org.alfresco.web.app.Application"%>
<%# page import="org.alfresco.web.ui.common.PanelGenerator"%>
when i click on Finish button i should have it disabled and the action function should be automatically fired like the following :
<td align="center">
<a4j:commandButton
id="finish-button" styleClass="wizardButton"
value="#{msg.finish_button}"
action="#{creationReclamationBean.terminerReclamation}"
onclick="this.disabled=true;"/>
</td>
The content of the function is the following :
public String terminerReclamation() throws SQLException {
if (!journeeServiceMetier.estJourOuvre(reclamationVO
.getReclamationEtape3VO().getDateReclamation())) {
Utils.addErrorMessage("La date de la demande "
+ reclamationVO.getReclamationEtape3VO()
.getDateReclamation()
+ " ne correspond pas à un jour ouvré ");
return null;
} else if (ireclamationServiceV4.ReclamationExiste(reclamationVO
.getOrdinal(), reclamationVO.getReclamationEtape3VO()
.getDateReclamation(), reclamationVO.getReclamationEtape3VO()
.getActivite().toString(), reclamationVO
.getReclamationEtape3VO().getProduitSelection().toString(),
reclamationVO.getReclamationEtape3VO()
.getOperationselectionne().toString(), reclamationVO
.getEtape1vo().getSiegeSelection(), reclamationVO
.getEtape1vo().getRacine())
&& !reclamationVO.isModeModif()) {
Utils.addErrorMessage("Cette réclamation existe déjà");
return null;
}
when i am debugging the code, the debugging process enters in the "else" conditional statement and the line below is executed but the message doesn't appear in my page.
previously when i used the following component :
<h:commandButton
id="finish-button" styleClass="wizardButton"
value="#{msg.finish_button}"
action="#{creationReclamationBean.terminerReclamation}"
onclick="this.disabled=true;"
/>
instead of a4j:commandButton the error message is displayed normally but the button is not disabled at all.
Can anyone of you give me a help
Thanks