[Mediawiki-l] Install problem - newbie

[Graham Mitchell]

Esteemed Mediawiki people
I've recently installed the latest stable distribution of Mediawiki on a
Mac OS X machine, mainly in order to learn how to use it. The Mac in
question is on a LAN sitting behind a NAT router on a DSL connection.
I installed according to the fairly brief instructions given with the
distribution, and it all went smoothly. I can see the wiki's Main Page
when I point my browser to the relevant page from the local machine.
Great.
However, when I try to see the wiki from outside the LAN, using the public
IP address all I get is an http 500 error message.
My router is set up to forward all port 80 requests through to the Mac
that is serving web pages, and this works perfectly for the rest of my
site (which includes a WordPress installation, suggesting that Apache,
MySQL and PHP are all set up and working as expected). Which leads me to
conclude that the problem lies within the Mediawiki configuration. I've
studied LocalSettings.php and DefaultSettings.php, and can find nothing
obvious. Then again, I'm no PHP expert. I imagine this must be a
reasonably common problem, but I can't find anything about it, and the
mailing list archive does not lend itself to searching.
Any pointers would be gratefully received.
Thanks

Graham