An error that leaves my WP page blank

I am getting the following error message:

Fatal error: Out of memory (allocated 24903680) (tried to allocate 300797 bytes) in /homepages/25/d299011628/htdocs/wp-includes/functions.php on line 252

Whilst I can see:
1. The side menu
2. The top menu
3. The WPMU add for the multisite content copier

I can see nothing else. The page is entirely blank.

What should I do?

Regards
Charles Vickers

WP Debug output for 3rd January:

WordPress Debug
----------

Operating System: Linux
Server: Apache
Memory usage: 31.74 MByte
MYSQL Version: 5.1.72-log
SQL Mode: Not set
PHP Version: 5.2.17
PHP Safe Mode: Off
PHP Allow URL fopen: Off
PHP Memory Limit: 256M
PHP Max Upload Size: 40M
PHP Max Post Size: 8M
PHP Max Script Execute Time: 900
PHP Exif support: Yes ( V1.4 )
PHP IPTC support: Yes
PHP XML support: Yes
Site URL: http://www.askit.co.uk
Home URL: http://www.politicaleconomy.me.uk
WordPress Version: 3.8
WordPress DB Version: 26691
Multisite: No
Active Theme: Arjuna X 1.7.1

Active Plugins
----------
Akismet: 2.5.9
All in One SEO Pack - Pro Version: 1.70
Bitly Official WordPress Plug-in: 1.1.0
Blog Protector: 4.8
Calls to Action: 1.2.5
Click To Tweet by Todaymade: 1.1
Debug Bar: 0.8.1
Fancy Excerpt: 3.3
FeedBurner FeedSmith: 2.3.1
Feed Facebook, Leave Facebook: 1.0
FeedWordPress: 2013.0504
FeedWordPress Duplicate Post Filter: 1.5
Google Analyticator: 6.4.7.1
Google XML Sitemaps: 3.4
Leads: 1.2.5
Login LockDown: v1.5
Recent Posts with Excerpts: 2.5
SABRE: 1.2.2
ShareThis: 7.0.8
Social: 2.11
Subscribe Remind: 1.3
Twitter Tools: 3.1
Updraft - Backup/Restore: 0.6.1
WordPress Database Backup: 2.2.4
WordPress Debug: 0.2.3
WP-Polls: 2.64
WP Google Analytics: 1.4.0
WP Open Graph: 1.5
WP to GHTime: 1.0.3

Inactive Plugins
----------
Landing Pages: 1.4.1
WordPress Mobile Edition: 3.1