On a fresh install of the FreePBX distro, I get a 404 (page not found) error when I click on one of the codecs under Settings -> Asterisk IAX Settings. The culprit appears to be line 187 in page.iaxsettings.php:
echo '<li><a href="a">'
Changing that to the following solved the problem:
echo '<li><a href="#">'
Thanks,
Lee