关于nginx+tomcat+memcached集群中session的问题：报错

在解决nginx+tomcat+memcached集群session的问题中，我在本机(Windows)测试，nginx+2个tomcat，将memcached添加到系统服务中并启动，分别添加memcached的jar包到tomcat的lib中，配置两个tomcat的context.xml，启动两个tomcat，访问页面报错，起初以为是版本的问题，换了好多版本的jar包，问题依旧，求高人指点。

context.xml配置如下：

<Manager className="de.javakaffee.web.msm.MemcachedBackupSessionManager"
        memcachedNodes="n1:127.0.0.1:11211"
        requestUriIgnorePattern=".*/.(png|gif|jpg|css|js)$"
        sessionBackupAsync="false"
        sessionBackupTimeout="100"
        transcoderFactoryClass="de.javakaffee.web.msm.serializer.javolution.JavolutionTranscoderFactory"
        copyCollectionsForSerialization="false" />

错误信息如下：

java.lang.NoSuchMethodError: net.spy.memcached.MemcachedClient.set(Ljava/lang/String;ILjava/lang/Object;)Lnet/spy/memcached/internal/OperationFuture;
	at de.javakaffee.web.msm.BackupSessionTask.storeSessionInMemcached(BackupSessionTask.java:227)
	at de.javakaffee.web.msm.BackupSessionTask.doBackupSession(BackupSessionTask.java:194)
	at de.javakaffee.web.msm.BackupSessionTask.call(BackupSessionTask.java:119)
	at de.javakaffee.web.msm.BackupSessionTask.call(BackupSessionTask.java:50)
	at de.javakaffee.web.msm.BackupSessionService$SynchronousExecutorService.submit(BackupSessionService.java:346)
	at de.javakaffee.web.msm.BackupSessionService.backupSession(BackupSessionService.java:205)
	at de.javakaffee.web.msm.MemcachedSessionService.backupSession(MemcachedSessionService.java:1059)
	at de.javakaffee.web.msm.RequestTrackingHostValve.backupSession(RequestTrackingHostValve.java:229)
	at de.javakaffee.web.msm.RequestTrackingHostValve.invoke(RequestTrackingHostValve.java:154)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:261)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:581)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
	at java.lang.Thread.run(Thread.java:619)