I've just run into a rather strange bug. I put together a simple HelloWorld type portlet using Spring MVC portlet, and after deploying it, it shows up and is displayable. However, when I click on refresh, the following exception is thrown:
14:15:22,367 ERROR [[PortalServlet]] Servlet.service() for servlet PortalServlet threw exception javax.servlet.ServletException: Unknown result org.jboss.portal.server.output.FragmentResult@19709b1 at org.jboss.portal.core.servlet.CoreServlet.render(CoreServlet.java:223) at org.jboss.portal.server.servlet.AbstractMainServlet.invoke(AbstractMainServlet.java:81) at org.jboss.portal.server.servlet.AbstractMainServlet.doGet(AbstractMainServlet.java:71) at javax.servlet.http.HttpServlet.service(HttpServlet.java:697) ....
For now I've found that by commenting out the <expiration-cache> setting in portlet.xml, it now works. But I'd really rather leave the caching on for performance reasons.