I found a solution in this thread: https://communities.netapp.com/thread/8473
- stop the NetApp vSphere Plugin Framework service,
- stop the NetApp SnapManager for Virtual Infrastructure service
- copy the %install%/smvi/server/repository/backups.xml file
- use wordpad and edit the same file
- remove the backup entry/ies starting from the "<backup uuid="" tag through to the </backup>
(may look like "<backup mounted="false" uuid=.....> )
- restart the SMVI and NVPF services