FileServerServlet IllegalStateException

java.lang.IllegalStateException
at org.apache.coyote.tomcat4.CoyoteResponseFacade.sendError(CoyoteResponseFacade.java:324)
at javax.servlet.http.HttpServletResponseWrapper.sendError(HttpServletResponseWrapper.java:162)

We're doing a response.sendError() after we've already started streaming data to the client. It's too late for the servlet container to back up and try again, so it blows up.