php warnings on every screen

I have moved a Buudypress (1.6) / WP (3.4.2) test installation from one server to another one (and what a job *that* was). Now I am getting php error messages of the form:
Warning: Creating default object from empty value in esp/wp-content/plugins/buddypress-group-documents/index.php on line 121
Warning: Creating default object from empty value in esp/wp-content/plugins/bp-groupblog/bp-groupblog.php on line 83
on every page in the Admin session. It's something in the server configuration but I'm stumped as to what.
I have:
Set wp-config.php define('WP_DEBUG', false);
Set /usr/local/etc/php.ini:

display_startup_errors = Off
log_errors = On
track_errors = Off
This *should* log errors to a log file (according to the comment in the ini file itself). The warning are in fact logged to an error log file via a VHOST in apache/extras/httpd-vhost.conf.
There are no error logging statements in the .htaccess file.
I am sure that the problem lies in the configuration of the current server (a FreeBSD Jail) but having checked the php.ini and wp-config.php I'm stumped as to where to look next.
Thanks for any help.