500 Servlet Exception

java.lang.IllegalStateException: forward() not allowed after buffer has
committed.
	at com.caucho.server.webapp.RequestDispatcherImpl.forward(RequestDispatcherImpl.java:141)
	at com.caucho.server.webapp.RequestDispatcherImpl.error(RequestDispatcherImpl.java:115)
	at com.caucho.server.webapp.ErrorPageManager.sendServletError(ErrorPageManager.java:361)
	at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:169)
	at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:226)
	at com.caucho.server.hmux.HmuxRequest.handleRequest(HmuxRequest.java:424)
	at com.caucho.server.port.TcpConnection.run(TcpConnection.java:477)
	at com.caucho.util.ThreadPool$Item.runTasks(ThreadPool.java:591)
	at com.caucho.util.ThreadPool$Item.run(ThreadPool.java:513)
	at java.lang.Thread.run(Thread.java:595)