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