Found the solution! Thanks to @XtremeBiker for the hints.
The <p:ajaxStatus onstart="statusDialog.show();" onsuccess="statusDialog.hide();"/>
is referencing a dialog box that I forgot to add in the XHTML. So I added the code below and it worked.
<p:dialog modal="true"
widgetVar="statusDialog"
header="Aguarde..."
draggable="false"
closable="false"
resizable="false"
width="245"
height="25" >
<div align="center">
<p:graphicImage value="/resources/images/ajax-loader.gif" />
</div>
</p:dialog>
I use this code to block screen when a ajax request is processing.
Thanks again.