This respone is when there are way too many requests for management operations on the cluster which are all getting queued up and all the queues to process any of the management operations is almost full.
This state must recover automatically after some time if not you can try the following,
* Check for the cluster health (cluster show).
* Check if all the cluster lifs are up and operational.
* May be run lun show -vserver <vserver name> (in case if there are way too many luns in the cluster). This will filter the request only to the vserver
* Check for Total management operations active on the cluster and wait for them to complete before trying "lun move".