ps2pdf and ghostscript

[Debian User <debian-user@zerocrossings.com>]

i am trying to convert a postscript file to a pdf file. when i run 
ps2pdf, i receive the following error (any suggestions?):

~$ ps2pdf filename.ps filename.pdf
Error: /undefined in $
Operand stack:

Execution stack:
   %interp_exit   .runexec2   --nostringval--   --nostringval--  
--nostringval--   2   %stopped_push   --nostringval--   --nostringval-
-   --nostringval--   false
   1   %stopped_push   1   3   %oparray_pop   1   3   %oparray_pop 
1   3   %oparray_pop   .runexec2   --nostringval--   --nostringval-
-   --nostringval--   2   %
stopped_push   --nostringval--   --nostringval--   --nostringval--
Dictionary stack:
   --dict:1037/1476(ro)(G)--   --dict:0/20(G)--   --dict:67/200(L)--
Current allocation mode is local
Current file position is 3
GNU Ghostscript 6.53: Unrecoverable error, exit code 1