I got that one yesterday on an AIX box.

In my case the server disk pool was too full.  (It may not be totally full,
but doesn't have enough free space to hold the largest thing that client
wants to send it - so some clients work, and some fail....)

Try this:

Do a Q NODE blah F=d, and look for the max mount points allowed.  If it is
set to 0, change it to 1.
UPDATE NODE BLAH MAXNUMMP=1

The if the problem is not enough space in the disk pool, the client will try
to mount a tape directly to finish the archive.

Even if you don't want to allow that on a regular basis, it will at least
verify what the problem is.....