500 Servlet Exception

[show] java.lang.IllegalStateException: sendError() forbidden after buffer has
been committed.

java.lang.IllegalStateException: sendError() forbidden after buffer has
been committed.
	at com.caucho.server.connection.AbstractHttpResponse.sendError(AbstractHttpResponse.java:496)
	at com.caucho.server.connection.AbstractHttpResponse.sendError(AbstractHttpResponse.java:477)
	at cn.dalian.web.servlet.VelocityServlet.error(VelocityServlet.java:54)
	at org.apache.velocity.tools.view.servlet.VelocityViewServlet.doRequest(VelocityViewServlet.java:426)
	at org.apache.velocity.tools.view.servlet.VelocityViewServlet.doGet(VelocityViewServlet.java:373)
	at cn.dalian.web.servlet.VelocityServlet.doGet(VelocityServlet.java:25)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:114)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:91)
	at com.caucho.server.dispatch.ServletFilterChain.doFilter(ServletFilterChain.java:103)
	at filters.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:170)
	at com.caucho.server.dispatch.FilterFilterChain.doFilter(FilterFilterChain.java:87)
	at com.caucho.server.webapp.WebAppFilterChain.doFilter(WebAppFilterChain.java:187)
	at com.caucho.server.dispatch.ServletInvocation.service(ServletInvocation.java:265)
	at com.caucho.server.http.HttpRequest.handleRequest(HttpRequest.java:273)
	at com.caucho.server.port.TcpConnection.run(TcpConnection.java:682)
	at com.caucho.util.ThreadPool$Item.runTasks(ThreadPool.java:730)
	at com.caucho.util.ThreadPool$Item.run(ThreadPool.java:649)
	at java.lang.Thread.run(Thread.java:619)