exceeding lisp pointer size?

[clemens fischer]

i got a warning from my trusty emacs-21 on freebsd:

  Warning: memory in use exceeds lisp pointer size
  Killing some buffers may delay running out of memory.
  However, certainly by the time you receive the 95% warning,
  you should clean up, kill this Emacs, and start a new one.

this is not always reproducable, but it usually happens when
pasting/yanking large (X-)selections (a few hundred lines).  it
happened specifically when answering a X509 related message in gnus
where i wanted to keep details of the certificate chain.  gnus message
mode sees the pgg generated verification result line and folds/unfolds
its contents, but the same problem appears when using Xclip(1) to
stash a large X-selection from a file and trying to paste it into some
emacs buffer.  emacs doesn't actually finish the yank, and it takes
about a minute before showing the warning.  nothing is lost and i can
keep using the (damaged?) emacs session, but i cannot get it to handle
kill items of size bigger than about 100 .. 200 lines!

whatever:  this is an emacs, not a gnus problem.  i would like to know
which variable i could frob to allow emacs more room.  my ~/.emacs
contains:

      ;;; Raise the default
      ;(setq gc-cons-threshold 1000000) ; 400000
      garbage-collection-messages nil
      max-specpdl-size 6555       ; Gnus
      max-lisp-eval-depth 555     ; default: 300
      kill-ring-max 133

i have browse-kill-ring and CUA-mode, and the warning has never
appeared before starting to use CUA-mode, _i think_!

thanks,

  clemens