The oncomplete
attribute is located on <a4j:support>
, not on the input component. Just move it to there and get rid of <a4j:support event="oncomplete">
which is never fired anyway.
<rich:comboBox value="#{myBean.myObj.name}"
defaultLabel="Please Select" status="defaultStatus"
valueChangeListener="#{myBean.validateNewValue}">
<f:selectItems value="#{myBean.nameList}" />
<a4j:support event="onchange" ajaxSingle="true" reRender="errTable,popUpPanel"
oncomplete="if(#{myBean.showPopup}) #{rich:component('popUpPanel')}.show();" />
</rich:comboBox>