PHP故障排除通知:未知:1 ...哪里是未知令牌?

I'm getting a PHP error which I need help to troubleshot:

[Fri May 08 10:20:41.234655 2015] [:error] [pid 6969] [client 207.183.229.82:3038] PHP Notice: Unknown: 1. h->opened_path=[null] h->filename=[/var/www/example.com/htdocs/wp-admin/network/site-new.php] in Unknown on line 0, referer: http://example.com/wp-admin/network/site-new.php

This occurs on a fresh installation of WordPress when I try to add a new site.

But what's the unknown token and why is it unknown? I've looked at line 0 of the file wp-admin/network/site-new.php, and it merely contains the start of a php tag: <?php

Additional Info

This error arises when I POST to a Wordpress action /wp-admin/network/site-new.php. This attempt actually adds 243 messages to my error log. Here are the first three:

[Fri May 08 10:20:41.234655 2015] [:error] [pid 6969] [client 207.183.229.82:3038] PHP Notice:  Unknown: 1. h-&gt;opened_path=[null]  h-&gt;filename=[/var/www/example.com/htdocs/wp-admin/network/site-new.php]
 in Unknown on line 0, referer: http://example.com/wp-admin/network/site-new.php
[Fri May 08 10:20:41.234716 2015] [:error] [pid 6969] [client 207.183.229.82:3038] PHP Notice:  Unknown: apc_cache_find [1627723]
 in Unknown on line 0, referer: http://example.com/wp-admin/network/site-new.php
[Fri May 08 10:20:41.235364 2015] [:error] [pid 6969] [client 207.183.229.82:3038] PHP Notice:  Unknown: 2. h-&gt;opened_path=[/var/www/example.com/htdocs/wp-admin/network/site-new.php]  h-&gt;filename=[/var/www/example.com/htdocs/wp-admin/network/site-new.php]
 in Unknown on line 0, referer: http://example.com/wp-admin/network/site-new.php