Hi, Using Seam 1.2.1.GA + JBoss AS 4.0.5.GA, I have a xhtml page with a datatable. The number of columns of this table is variable. I use a jstl <c:foreach> in this datatable like this: <h:form id="MyForm"> | ... | <h:dataTable value="#{bean.var}" var="lineSimple"> | <h:column> | <f:facet name="header"> | <h:outputText value="Activite" /> | </f:facet> | <h:outputText value="#{lineSimple.lineDesignation}"/> | </h:column> | | <c:forEach items="#{bean.var.columnDataModel.wrappedData}" | var="columnSimple"> | <h:column> | <f:facet name="header"> <h:outputText value="#{columnSimple.columnDesignation}"/> | </f:facet> | <h:inputText value="#{lineSimple.cellList[columnSimple.columnId].cellValue}"/> | ... | </c:forEach> | ... | </h:form> All this is in a form with other inputs. My page uses a template with an Ajax menu that is also in a form. When I change the values of my inputs, the number of columns of the table increases. When I do it once it's ok but when I do it again I have this error: duplicate Id for a component MyForm:_id914:_id44 View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4100546#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...