psnup creating faulty PS?

[Debian Mail <debian@sos.ethz.ch>]

I have a PDF document which I printed to a PS File on windows NT. I
used fixps to repair the NT errors. Then I used psresize to scale the
document to a4. The resulting file can be viewed with gs without
problem. But when I use psnup -4 -d on the file, the resulting PS
cannot be printed or viewed with gs anymore. It gives me the following
error messages:

Error: /invalidaccess in def
Operand stack:
   showpage   --nostringval--
Execution stack:
   %interp_exit   .runexec2   --nostringval--   --nostringval--   --nostringval--   2   %stopped_push   --nostringval--   --nostringval--   --nostringval--   false   1   %stopped_push   1   3   %oparray_pop   .runexec2   --nostringval--   --nostringval--   --nostringval--   2   %stopped_push   --nostringval--   --nostringval--   --nostringval--
Dictionary stack:
   --dict:907/941(G)--   --dict:0/20(G)--   --dict:66/200(L)--   --dict:35/100(L)--   --dict:70/86(L)--   --dict:112/150(L)--   --dict:74/75(L)--   --dict:10/38(L)--
Current allocation mode is local
Current file position is 587672
Aladdin Ghostscript: Unrecoverable error, exit code 1


Has anybody an idea what could be wrong here?

Stef