I just did a nice fresh install of Elastix 2.3, from the ISO posted at elastix.org. I try using the FreePBX admin panel, but when I click the PBX button in freepbx, i get nasty errrors from PHP about how it cannot access /etc/amportal.conf.

the file exists. It has user:group permissions of asterisk:asterisk, and i tried in my own feeble way to change the permissions to 660 or 666, but no dice, still get this nasty error, which prevents Freepbx from configuring the system.

how can a production version of elastix, presumably used by 100,000+ people, have such a fundamental error in it?

I think that the error is due to the fundamental characters that you have used...
I don't remember very well, but freepbx doesn't like to parse some special characters, not sure if it was % or &