Portlet caching issue may occurred when calling portletResponse.getPortletOutputStream()

If portlet caching is enabled and you calling portletResponse.getPortletOutputStream() it will throw exceptions.
To resolve this -
1) Either disabled the portlat caching and restart the portal server
2) Install the fix pack http://www-01.ibm.com/support/docview.wss?uid=swg1PK93614