Nothing of interest in the logs but I think I found the problem.
These pages previously resided on an IIS web server. The php pages are descended from ASP pages on the original site. When redeveloping the site as PHP/MySQL the following two lines which appeared at the top of all my pages caused problems -
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "DTD/xhtml1-strict.dtd">
Strange thing is, they never caused a problem in the html pages and, for the last month, have worked quite happily on a Gentoo Linux/Apache webserver. If I now remove those lines from the problem pages they work fine. Is it possible the version of apache e-smith uses has a problem with that code? Gentoo is pretty bleeding edge (one of the reasons I am switching to SMES) so I was probably using a more recent apache version on that. Alternately, is there a config setting in apache that affects this?
Thanks for your help.
Cheers,
Allan