Joni - I'm NAS-impaired, but you need to do basic looksee... Do 'dsmc Query Filespace' to see what viable filespaces the client generally has. Also do 'Query NASBAckup' in the TSM server to see what it specifically has.
Pay particular heed to what the Unix client manual says about the restorability of Full NAS images, in its documentation of the MODE option. This may well be your problem. Richard Sims