500 Servlet Exception

java.lang.IllegalStateException: forward() not allowed after buffer has
committed.
	at com.caucho.server.webapp.RequestDispatcherImpl.forward(RequestDispatcherImpl.java:139)
	at com.caucho.server.webapp.RequestDispatcherImpl.error(RequestDispatcherImpl.java:113)
	at com.caucho.server.webapp.ErrorPageManager.sendServletError(ErrorPageManager.java:354)
	at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:165)
	at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:208)
	at com.caucho.server.hmux.HmuxRequest.handleRequest(HmuxRequest.java:396)
	at com.caucho.server.port.TcpConnection.run(TcpConnection.java:363)
	at com.caucho.util.ThreadPool.runTasks(ThreadPool.java:490)
	at com.caucho.util.ThreadPool.run(ThreadPool.java:423)
	at java.lang.Thread.run(Thread.java:595)