Hi,
I heaved the same problem,
the issue was - on the (RLM/SP) shell- it was connected true this shell to the vfiler, (vfiler context <vfilername>
you will need to connect to the SP/RLM and verify that you don't connected to the vfiler on this shell
if you are connected to the vfiler you will need to run from this shell "vfiler context vfiler0"
and this will solved your problem now you can try one more time 🙂 to do the vfiler delete or destroy!
also reboot to the system or cf takeover will solved this issue 🙂 but you don't need to do it!!!
best regards,
Kfir