Sell role went down after 24 to 32 hours with Illegal state exception :Timed out waiting to add Cmd

Current release, we had enabled write to couchbase turned ON. Couchbase regression was fine in QA and PE env. It was fine even in Production intially, but after 24 to 30 hours of deployemnt, we started seeing below exceptions and blade went down. Sell flow was redirecting to error page.
Need to know why is this happening. Once we restart the application server exception doesnt show up.
But we are sure, it will start happening soon

2014-10-02 00:26:34,000 [c49a#1061c/https:///sell/] priority=ERROR app_name=stubhubSLXRole thread=ajp-0.0.0.0-8009-41 location=NewAccessControlHandler line=175 Exception
java.lang.IllegalStateException: Timed out waiting to add Cmd: 1 Opaque: 1147840 Key: com.stubhub.user.business.entity.UserSession|63C21A07311389A1EC361D834BF46E72 Cas: 0 Exp: 7200 Flags: 1 Data Length: 1748(max wait=10000ms)
at net.spy.memcached.protocol.TCPMemcachedNodeImpl.addOp(TCPMemcachedNodeImpl.java:362)
at net.spy.memcached.MemcachedConnection.addOperation(MemcachedConnection.java:1267)
at com.couchbase.client.CouchbaseConnection.addOperation(CouchbaseConnection.java:277)
at net.spy.memcached.MemcachedConnection.enqueueOperation(MemcachedConnection.java:1185)
at net.spy.memcached.MemcachedClient.asyncStore(MemcachedClient.java:328)
at net.spy.memcached.MemcachedClient.set(MemcachedClient.java:929)
at com.stubhub.common.cache.store.couchbase.CouchbaseStore.put(CouchbaseStore.java:148)
at com.stubhub.common.cache.store.CompositeCacheStore.put(CompositeCacheStore.java:69)
at com.stubhub.common.session.impl.UserSessionCacheManagerImpl.putCrossModuleValue(UserSessionCacheManagerImpl.java:48)
at com.stubhub.user.business.manager.impl.UserSessionCacheMgrImpl.putUserSessionToStore(UserSessionCacheMgrImpl.java:269)
at com.stubhub.user.business.manager.impl.UserSessionCacheMgrImpl.createUserSession(UserSessionCacheMgrImpl.java:806)
at sun.reflect.GeneratedMethodAccessor1305.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:318)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at com.stubhub.common.util.StubHubPerformanceMonitorInterceptor.invoke(StubHubPerformanceMonitorInterceptor.java:28)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:90)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:202)
at $Proxy725.createUserSession(Unknown Source)
at com.stubhub.user.business.facade.impl.UserSessionFacadeImpl.createUnidentifiedSession(UserSessionFacadeImpl.java:564)
at com.stubhub.user.business.facade.impl.UserSessionFacadeImpl.createUnidentifiedSession(UserSessionFacadeImpl.java:94)
at sun.reflect.GeneratedMethodAccessor1297.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:318)
at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:183)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)