Cannot access network admin panel

I have a fresh install of WP multisite with half a dozen blogs configured. I can access all of these and their control panels but I cannot access the network dashboard. The page I am trying to access is:

http://54.171.135.229/wp-admin/network/plugins.php

I clearly could at some point because I have setup the sites.

The message I see is as follows:

Google Chrome could not load the webpage because 54.171.135.229 took too long to respond.

I have checked that Apache logs and there isn’t anything related to this there. I did also wonder if it is the .htaccess file but I cannot see anything obvious:

RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
#RewriteRule  ^[_0-9a-zA-Z-]+/(wp-(content|admin|includes).*) $1 [L]
#RewriteRule  ^[_0-9a-zA-Z-]+/(.*\.php)$ $1 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]

#### To block getting crawled by semalt.com, evil-spam-domain.com etc. added below lines by Neelesh 13.6.2014

SetEnvIfNoCase Via evil-spam-proxy spammer=yes
SetEnvIfNoCase Referer evil-spam-domain.com spammer=yes
SetEnvIfNoCase Referer evil-spam-keyword spammer=yes
SetEnvIfNoCase Via pinappleproxy spammer=yes
SetEnvIfNoCase Referer semalt.com spammer=yes
SetEnvIfNoCase Referer poker spammer=yes

Order allow,deny
Allow from all
Deny from env=spammer

######################## End \Semalt.com ######

Anyone any ideas where to look next?