h:ajax tag problem. The datagrid doesn't reload

Question

This is my Code. It does not work for me. But it works in the solution of a friend. I don't know whats the reason. I don't get any error. All seems to be fine. But if I click my radiobutton nothing happens.

<h:form id="form">
            <h:panelGrid id="baseData" columns="2">
                <h:selectOneRadio value="#{billing.paymentType}" id="paymentType">
                    <f:selectItem itemValue="cred" itemLabel="credicard" />
                    <f:selectItem itemValue="bill" itemLabel="bill" />
                    <f:ajax render="credinfo" />
                </h:selectOneRadio>
            </h:panelGrid>
            <h:panelGrid id="credinfo"  columns="2">
                <h:outputText value="bla" rendered="#{billing.paymentType=='cred'}"/>
            </h:panelGrid>
        </h:form>

Now i works.. I don't know why.