java.lang.ClassCastException: org.apache.pluto.internal.impl.RenderRequestImpl

Hi, I'm trying to implement my own portal and I'm getting the following 
exception when container.doRender() is called:

[DEBUG] PortletInvoker - Dispatching to portlet servlet at: /PlutoInvoker/Hello
java.lang.ClassCastException: org.apache.pluto.internal.impl.RenderRequestImpl
         org.apache.pluto.core.PortletServlet.dispatch(PortletServlet.java:196)
         org.apache.pluto.core.PortletServlet.doGet(PortletServlet.java:143)
         javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
         javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
         org.apache.pluto.core.PortletInvoker.invoke(PortletInvoker.java:169)
         org.apache.pluto.core.PortletInvoker.render(PortletInvoker.java:111)
         org.apache.pluto.core.PortletContainerImpl.doRender(PortletContainerImpl.java:158)
         br.com.myportal.servlets.MainServlet.doGet(MainServlet.java:37)
         javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
         javax.servlet.http.HttpServlet.service(HttpServlet.java:802)


PortletServlet.java, line 196:
portletRequest = (InternalPortletRequest) 
request.getAttribute(Constants.PORTLET_REQUEST);

I can't understand why this line is throwing ClassCastException, 
RenderRequestImpl implements InternalPortletRequest!