difficulty with copy-bits

[ferrante@world.std.com (Richard D Ferrante)]

Whenever I try to do a copy-bits MCL2.0p3 quits, MacsBug claims
Bus Error at 40800E2 _BitsToMap +0010
while reading long word from FFFFFFFF in user data space
 a simple example appears below

(defun self-copy-test (&optional (a-window *test-window*))
  (when (typep a-window 'window)
    (with-focused-view  a-window
      (format t "~% Test window ~a" a-window)
      (rlet ((source-r :rect
                       :topleft #@(0 0)
                       :bottomright #@(160 5)
                       )
             (dest-r :rect
                     :topleft #@(0 20)
                     :bottomright #@(160 30)))
        (copy-bits (rref (wptr a-window) CGrafPort.portPixMap)
                   (rref (wptr a-window) CGrafPort.portPixMap)
                   source-r dest-r)))))

My current configuration is a IIci 20M Ram 33MVirtual system 7.0*(with
tune up).
The display is a Radius 19" 8 bit grayscale monitor/board.

I must be doing something wrong but can't figure out what it is, any
help would be appreciated.

Thanks

--- 

Richard Ferrante
(617)-739-7055
ferrante@world.std.com