>    After many tries at fixing this we gave up and wrote the /netbsd
>    file to a new tape (yes the tape drive worked, a bit slowly, but
>    worked all the same). I am using this to boot at the moment. Any

Yes, I think you found a but in bim.  It doesn't report when it can't
write the disklabel.  (At least this might be the problem.)

Try:

  disklabel -W sdX   (Make the disklabel writeable)
  bim ...

--Phil

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