Hello,
I am guessing your Networker server is out of sync with the VTL, stop any 
running processes and issue nsrck -HE -vvv and reinventroy, if it keeps 
happening again and again, you may have to run frequent inventory , we are 
battling this issue with Networker and NetApp VTL  right now, make sure 
you have persistent  binding enabled & double check your configuration to 
make sure there are no there issues. You may want to run the groups with 
additional diagnostics to see if there are any issues identified.
Eventually, you will need to work closely with EMC  to sort out your 
troubles, to date they have not offered any solutions.
Thanks

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