[SM-STABLE] login attempt gives strange error

[Andrew S. J. <new...@ar...>]

I've recently installed squirrelmail on my FreeBSD machine and
everything seemed to be going swimmingly until I tried to log in to view
my mail. I can see the squirrelmail login screen fine but when I enter
my user ID and password, I am redirected to the URL
'http://www.mydomain.com/squirrelmail/src/redirect.php' and this is the
message that appears at the top of the screen:

Warning: Failed opening '/squirrelmail/functions/page_header.php' for
inclusion (include_path='.:/usr/local/lib/php') in
/usr/local/squirrelmail/functions/display_messages.php on line 99

The rest of the screen looks like a standard squirrelmail screen and
says 'ERROR  You must be logged in to access this page.  Go to login
page'.

This happens when I use either Netscape 4.79 or IE 5.

Here are the versions of various software I'm running:

FreeBSD 4.5
apache 2.0.36
mod_php4 4.2.1
squirrelmail 1.2.6

I've installed the various software from the ports tree of my FreeBSD
box. Apache itself if running fine as I can browse other pages without
problems. I don't have any pages other than squirrelmail that use php
however.

I've gone through the squirrelmail install document and the FAQ on the
squirrelmail website and I think I've covered all the easy stuff. I've
edited my httpd.conf file and added the lines as prescribed in the
squirrelmail INSTALL document. I've also created a php.ini file and put
it in /usr/local/lib. Here it is:

session.use_cookies = 1
session.save_path = /var/php-session
register_globals = On
file_uploads = On

I've set up an alias in my httpd.conf file for squirrelmail. Here are
the relavent lines:

Alias /squirrelmail "/usr/local/squirrelmail"
<Directory "/usr/local/squirrelmail">
    Options Indexes FollowSymLinks MultiViews
    AllowOverride All
    Order allow,deny
    Allow from all
</Directory>

I've been through the squirrelmail configure script and set everything
up to what I think it should be. I've also ensured that my browser is
using cookies. Did I mention that I can access my IMAP server just fine
using a regular mail client from either the local or a remote machine?

One thing that did cause problems. When I created a .htaccess file in
the squirrelmail directory (as described in the squirrelmail INSTALL
document) I would get an error 404 from my browser. When I deleted this
file, I was able to access the squirrelmail login screen again. The
INSTALL document says the .htaccess file should contain these lines:

    AddType application/php4script .php
    Action application/php4script /cgi-bin/php

There is no php file or directory in cgi-bin but there is a php
directory in /usr/local/lib.

By the way, I've installed the bug_report plugin but since I can't log
in to squirrelmail, I can't turn it on.

If anyone has any ideas what's going on, I would really like to know.

Andrew