To troubleshoot this issue, add the ncpcon dismount <volumeName> command in the cluster unload script before nss /pooldeac command. For example,
del secondary ipaddress 10.10.102.111
CLUSTER CVSBIND DEL NSS_CLUSTER_DDDD_SERVER 10.10.102.111
NUDP DEL NSS_CLUSTER_DDDD_SERVER 10.10.102.111
ignore_error ncpcon dismount dvol
nss /pooldeactivate=DDDD /overridetype=question
Add this command for all the volumes.