Reading IRIS inst tapes remotely from Sun?

[aem at mthvax.cs.miami.edu]

Well, we got a Personal Iris without a tape drive, thinking we'd be able
to read tapes off of one of our tape-equipped Suns. inst, however, doesn't
want to cooperate. I verified all of the permissions back and forth
between the sun and the iris, and both ways it passed the test in the Iris
manual (rsh hostname date ). Yet whenever I try to use inst to read the
tape it comes up with "Permission denied." twice. 

a) is it possible to read iris "inst" format tapes remotely from a Sun?
b) how? I'm baffled, and the manual doesn't help (and the SGI salesman is
   apparently on vacation).

aem at mthvax.cs.miami.edu