Do you happen to have any Xendesktop PVS or MCS virtual macghines on this volume? I have the same problem and Snapcenter cannot backup any nfs luns where I have MCS configured machines.
One thing to try..goto the VM's that are not working in the vcenter web client and try and try selecting individual VM's and see if it will let them select for Snapcenter protection. My MCS VM's won't let me select them. It could be because i have GRID cards added to those VM's but no one knows yet...still working through my case.
After lot of debug with NetApp support two things as appeared:
You can't include a VM in a backup Job if this VM has some disks outside the NetApp Scope. In my case my faulty VM has one of his disks (Sowftware backup) stored on a Synology NAS. So you have the message saying that this entitie has an issue.
Second issue: i can't contact the vCenter Host plugin because the host is hosted in another site with routing between. No connection could be made because the target machine actively refused it 10.x.x.x:8144 Nothing is preventing this connection, and if i try to do TCP port check or Telnet it's working but not with NetApp SnapCenter. No Answer Why! I have just moved the plugin host to the same site of SnapCenter Host and it's working.