error in solr operation

There was a problem: org.apache.solr.core.SolrException: ERROR:unknown field 'title' at org.apache.solr.update.DocumentBuilder.addField(DocumentBuilder.java:95) at org.apache.solr.update.DocumentBuilder.addField(DocumentBuilder.java:75) at org.apache.solr.handler.XmlUpdateRequestHandlerStax.readDoc(XmlUpdateRequestHandlerStax.java:337) at org.apache.solr.handler.XmlUpdateRequestHandlerStax.processUpdate(XmlUpdateRequestHandlerStax.java:172) at org.apache.solr.handler.XmlUpdateRequestHandlerStax.update(XmlUpdateRequestHandlerStax.java:377) at org.apache.solr.handler.XmlUpdateRequestHandlerStax.doLegacyUpdate(XmlUpdateRequestHandlerStax.java:389) at org.apache.solr.servlet.SolrUpdateServlet.doPost(SolrUpdateServlet.java:59) at javax.servlet.http.HttpServlet.service(HttpServlet.java:616) at javax.servlet.http.HttpServlet.service(HttpServlet.java:689) at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:428) at org.mortbay.jetty.servlet.WebApplicationHandler$CachedChain.doFilter(WebApplicationHandler.java:830) at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:137) at org.mortbay.jetty.servlet.WebApplicationHandler$CachedChain.doFilter(WebApplicationHandler.java:821) at org.mortbay.jetty.servlet.WebApplicationHandler.dispatch(WebApplicationHandler.java:471) at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:568) at org.mortbay.http.HttpContext.handle(HttpContext.java:1530) at org.mortbay.jetty.servlet.WebApplicationContext.handle(WebApplicationContext.java:633) at org.mortbay.http.HttpContext.handle(HttpContext.java:1482) at org.mortbay.http.HttpServer.service(HttpServer.java:909) at org.mortbay.http.HttpConnection.service(HttpConnection.java:820) at org.mortbay.http.HttpConnection.handleNext(HttpConnection.java:986) at org.mortbay.http.HttpConnection.handle(HttpConnection.java:837) at org.mortbay.http.SocketListener.handleConnection(SocketListener.java:245) at org.mortbay.util.ThreadedServer.handle(ThreadedServer.java:357) at org.mortbay.util.ThreadPool$PoolThread.run(ThreadPool.java:534)