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:362)
	at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:175)
	at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:229)
	at com.caucho.server.hmux.HmuxRequest.handleRequest(HmuxRequest.java:420)
	at com.caucho.server.port.TcpConnection.run(TcpConnection.java:514)
	at com.caucho.util.ThreadPool.runTasks(ThreadPool.java:527)
	at com.caucho.util.ThreadPool.run(ThreadPool.java:449)
	at java.lang.Thread.run(Thread.java:662)