莫名其妙的 java.lang.NoSuchMethodError

求大侠帮忙：我在servlet中调用dao中的方法，抛出以下异常，但是我是在同一个servlet中调用同一个dao中的另一个方法却正常运行，不存在类没有导入的问题，方法名也正确，郁闷了半天还是没有结果严重: Servlet.service() for servlet SaleServlet threw exception
java.lang.NoSuchMethodError: cn.wjt.dao.SaleDao.getLastSale()Lcn/wjt/vo/SaleBills;
at cn.wjt.servlet.SaleServlet.queryLastItem(SaleServlet.java:73)
at cn.wjt.servlet.SaleServlet.doPost(SaleServlet.java:34)
at cn.wjt.servlet.SaleServlet.doGet(SaleServlet.java:29)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at cn.wjt.filter.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:44)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:857)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Thread.java:619)