Hi,
The error is expected, it is one of the requirement for vol-move:
# The source volume should not be exported to NFS or CIFS clients when the volume move operation is in progress.
https://library.netapp.com/ecmdocs/ECMP1196995/html/GUID-09E9890C-EFD4-47EA-9539-A658FD251C93.html
I would call it a disruptive process for NAS protcols (NFS/CIFS), as you will be required to stop NFS exports or CIFS, which means a 'downtime' during the move period.
You have two options 'volmove' or 'snapmirror' : Advantage of vol-move over SnapMirror is that, you do not have to update the exports or re-create the shares. However, with snapmirror, the control is on you, once base replication is done, you can chose a maintenance window, termiante cifs, final update and re-create shares.
In any case, downtine is needed in both case, choice is yours.