I finally stumbled onto the answer. Plugging in the error message to google, I discovered that this has something to do with having installed an X11 update at one point (I had done this out of desperation when copy/paste stopped working correctly with the release of SE 1400, and it of course did not fix that problem -- bad move on my part all around).
Apparently this newer version of X11 is broken after an Apple security update is applied (nice!).
So, re-installing the newer version (2.5.0) of X11 fixes the problem. The newer version is available here:
http://xquartz.macosforge.org/trac/wiki/ReleasesI assume the X11 installer must touch something outside of the X11 app directory, since otherwise deleting and reinstalling from the Leopard disk would have fixed the problem.
So, I would suggest folks don't install 2.5.0 unless you have a good reason to. Once you install it, it is apparently very difficult to revert. And the X11 site says:
"Mac OS-X Updates (Leopard Only): You will need to re-install this package after future OS, and Security Updates delivered through Apple's Software Update. Additionally, you should reinstall this package after installing XCode."
Reminds me of the common .dll shenanigans I used to have to work around in Windows all the time... ugggh!
- Slim.