Dear stuartr-2,
1. Try adding this line to your wp-config.php file:
define('WP_MEMORY_LIMIT', '128M');
2. If you have access to your PHP.ini file, change the line in PHP.ini
If your line shows 32M try 128M:
memory_limit = 128M ; Maximum amount of memory a script may consume (128MB)
3. If you don't have access to PHP.ini try adding this to an .htaccess file:
php_value memory_limit 128M
this video might be helpul:
http://www.youtube.com/watch?v=s7PPnlJnNOg
4. Talk to your host.
More info:
http://codex.wordpress.org/Editing_wp-config.php#Increasing_memory_allocated_to_PHP
Please let me know if you are satisfied with my answer and if I can help you with any other questions you might have.