What you did earlier was a so-called '3rd-party restore'. You can do this but 
of course you must have at least 2 filers to achieve that. 

NDMP type backups must be recovered from a compatible device, in this case a 
NDMP tape drive.
With only one filer left you have only one choice: attach the tape drives to 
the filer and configre them as NDMP tape drives.

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