Rebalance failure when Online upgrading from 180 to 181 (Rebalance exited with reason {wait_for_memcached_failed,"bucket-1",)

Test case that failed
upgradetests.MultipleNodeUpgradeTests.test_upgrade,initial_version=1.8.0r-55,create_buckets=True,insert_data=True,start_upgraded_first=True,load_ratio=10,online_upgrade=True

[ns_server:info] [2012-05-07 22:01:20] [ns_1@10.3.121.92:<0.18886.1>:diag_handler:log_all_tap_and_checkpoint_stats:123] logging tap & checkpoint stats
[ns_server:debug] [2012-05-07 22:01:20] [ns_1@10.3.121.92:ns_config_log:ns_config_log:log_common:111] config change:
counters ->
[

{rebalance_fail,1}

,

{rebalance_start,5}

,

{rebalance_success,4}

]
[error_logger:error] [2012-05-07 22:01:20] [ns_1@10.3.121.92:error_logger:ale_error_logger_handler:log_msg:76] Error in process <0.30188.0> on node 'ns_1@10.3.121.93' with exit value: {undef,[

{diag_handler,log_all_tap_and_checkpoint_stats,[]}]}


[error_logger:error] [2012-05-07 22:01:20] [ns_1@10.3.121.92:error_logger:ale_error_logger_handler:log_msg:76] Error in process <0.29943.0> on node 'ns_1@10.3.121.95' with exit value: {undef,[{diag_handler,log_all_tap_and_checkpoint_stats,[]}

]}

[error_logger:error] [2012-05-07 22:01:20] [ns_1@10.3.121.92:error_logger:ale_error_logger_handler:log_msg:76] Error in process <0.29932.0> on node 'ns_1@10.3.121.98' with exit value: {undef,[

{diag_handler,log_all_tap_and_checkpoint_stats,[]}]}


[error_logger:error] [2012-05-07 22:01:20] [ns_1@10.3.121.92:error_logger:ale_error_logger_handler:log_msg:76] Error in process <0.30010.0> on node 'ns_1@10.3.121.97' with exit value: {undef,[{diag_handler,log_all_tap_and_checkpoint_stats,[]}

]}

[ns_server:debug] [2012-05-07 22:01:20] [ns_1@10.3.121.92:ns_config_events:ns_node_disco_conf_events:handle_event:56] ns_node_disco_conf_events config all
[ns_server:debug] [2012-05-07 22:01:20] [ns_1@10.3.121.92:ns_config_rep:ns_config_rep:handle_info:201] Pushing config
[ns_server:debug] [2012-05-07 22:01:20] [ns_1@10.3.121.92:ns_config_rep:ns_config_rep:handle_info:203] Pushing config done
[ns_server:debug] [2012-05-07 22:01:20] [ns_1@10.3.121.92:ns_config_log:ns_config_log:log_common:111] config change:
rebalancer_pid ->
undefined
[ns_server:debug] [2012-05-07 22:01:20] [ns_1@10.3.121.92:ns_config_log:ns_config_log:log_common:111] config change:
rebalance_status ->

{none,<<"Rebalance failed. See logs for detailed reason. You can try rebalance again.">>}

[ns_server:debug] [2012-05-07 22:01:20] [ns_1@10.3.121.92:ns_config_events:ns_node_disco_conf_events:handle_event:56] ns_node_disco_conf_events config all