ns_server_error: Deleting some old copies of vbucket failed errors

When running automation for new rebalance seeing bunch of errors as following:-

[ns_server:error] [2012-04-12 11:06:26] [ns_1@10.1.3.74:<0.23616.35>:ns_vbucket_mover:handle_info:145] Deleting some old copies of vbucket failed: [{undefined,
{'EXIT',
{{nodedown,undefined},
{gen_server,call,
[

{'ns_memcached-default', undefined}

,

{delete_vbucket,672}

,
30000]}}}}]