è so exibir este modal panel, apos vc lancar a mensagem/erro
<a4j:outputPanel ajaxRendered="true">
<rich:modalPanel id="errorPanel" autosized="true" width="350"
styleClass="erro"
showWhenRendered="#{facesContext.maximumSeverity !=null}">
<f:facet name="header">
<h:outputText value="Informação" />
</f:facet>
<f:facet name="controls">
<h:panelGroup>
<h:graphicImage value="/images/close.png" id="hidelink9" />
<rich:componentControl for="errorPanel" attachTo="hidelink9"
operation="hide" event="onclick" />
</h:panelGroup>
</f:facet>
<h:form id="frmErro">
<center>
<table>
<tr>
<td><rich:messages layout="list" showSummary="true"
id="errMsg" errorClass="erro" infoClass="info">
<f:facet name="errorMarker">
<h:outputText value=" " />
</f:facet>
<f:facet name="warnMarker">
<h:outputText value=" " />
</f:facet>
<f:facet name="infoMarker">
<h:outputText value=" " />
</f:facet>
</rich:messages></td>
</tr>
<tr>
<td align="center"><a4j:commandButton action="#" value=" OK "
immediate="true" limitToList="true" ajaxSingle="true"
styleClass="btn" onclick="Richfaces.hideModalPanel('errorPanel')">
</a4j:commandButton></td>
</tr>
</table>
</center>
</h:form>
</rich:modalPanel>
</a4j:outputPanel>