I can add up to 17 items to my Menu. As soon as I add one more item by clicking the checkbox for the page that I want to add in the Pages box in the left hand column and save the menu, the item that is last in the list drops off.
The Appearance Menus Screen page in the Wordpress codex makes no mention of this limit.
I am using a child theme of the Thematic theme; but I have had this problem before with other themes too.
If there is a limit, is there anything that I can do to override this?
Could possibly be this bug http://core.trac.wordpress.org/ticket/14134 and http://wordpress.org/support/topic/rc32-menus-still-crippled?replies=28 but 17 menu items is very low threshold.
Try raising your php memory allocation using FTP:
1) You can edit the memory_limit line in your php.ini (if you have access to that file) to 64M:
memory_limit = 64M;
2) If you can't get to the php.ini file, add this line at the top of your .htaccess file:
php_value memory_limit 64M
3) If that doesn't work or throws a "500 Internal Server Error", delete the line from .htaccess.
Then try adding the line below near the top of your wp-config.php file, right after the opening <?php
define('WP_MEMORY_LIMIT', '64M');
If you have a php.ini, also check and raise the execution time limits:
max_execution_time = 600
max_input_time = 600
If the server is running suhosin, try these new limits:
suhosin.post.max_vars = 5000
suhosin.request.max_vars = 5000
