Mac OS X Leopard v10.5 (MB427Z/A)

The process has forked and you cannot use this CoreFoundation

http://developer.apple.com/releasenotes/CoreFoundation/CoreFoundation.html

CoreFoundation and fork() Due to the behavior of fork(),
CoreFoundation cannot be used on the child-side of fork(). If you
fork(), you must follow that with an exec*() call of some sort, and
you should not use CoreFoundation APIs within the child, before the
exec*(). The applies to all higher-level APIs which use
CoreFoundation, and since you cannot know what those higher-level APIs
are doing, and whether they are using CoreFoundation APIs, you should
not use any higher-level APIs either. This includes use of the
daemon() function.

Additionally, per POSIX, only async-cancel-safe functions are safe to
use on the child side of fork(), so even use of lower-level
libSystem/BSD/UNIX APIs should be kept to a minimum, and ideally to
only async-cancel-safe functions.

This has always been true, and there have been notes made of this on
various Cocoa developer mailling lists in the past. But CoreFoundation
is taking some stronger measures now to "enforce" this limitation, so
we thought it would be worthwhile to add a release note to call this
out as well. A message is written to stderr when something uses API
which is definitely known not to be safe in CoreFoundation after
fork(). If file descriptor 2 has been closed, however, you will get no
message or notice, which is too bad. We tried to make processes
terminate in a very recognizable way, and did for a while and that was
very handy, but backwards binary compatibility prevented us from doing
so.

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This is the function you set a debug breakpoint on if you try to fork() in Leopard then call a CoreFoundation method:

void __THE_PROCESS_HAS_FORKED_AND_YOU_CANNOT_USE_THIS_COREFOUNDATION_FUNCTIONALITY___YOU_MUST_EXEC__(void);