bug: image zooming not work

["Samuel Wales" <samologist@xxxxxxxxx>]

M-[ and M-] produce wrong-type argument stringp, nil.  Here is the
stack trace.  w3m 0.5.2, Carbon Emacs 22, Mac OS X Tiger.

  start-process(nil #<buffer  *w3m-work*<5>> nil "-resize" "150%"
"/Users/sam/.w3m/w3mel5848qFp" "-")
  apply(start-process nil #<buffer  *w3m-work*<5>> nil ("-resize"
"150%" "/Users/sam/.w3m/w3mel5848qFp" "-"))
  w3m-process-start-process(((nil "-resize" "150%"
"/Users/sam/.w3m/w3mel5848qFp" "-") . [w3m-process-object #<buffer
*w3m-work*<5>> nil ([#<buffer  *w3m-work*<5>> #<buffer *w3m*> ...
nil])]))
  w3m-zoom-in-image(nil)
  call-interactively(w3m-zoom-in-image)

Any idea what this might be?

Thanks.