I have a mega options page that has 70 fields and works fine. When I added 2 more fields (72 total) I started getting the “No Custom Field Group found for the options page.” message. Despite there being a group assigned 2 seconds earlier.
Creating a new fields group assigned to the Options page removed the error, but the large group didn’t show — so I tracked it. Still no luck.
Re-saved the group, changed the location options, saved, changed them back, no luck.
Removing 2 items from the large group restored the option page functionality.
I get that there has to be some limit, but 70 seems a bit arbitrary and more like a bug than a performance issue? 😉
Silly me, of course the answer was not number of fields, but number of post vars…
72 fields just happened to push the post vars count over PHP 5’s default limit of 1000. This issue also crops up with really large menus in WP.
The fix:
Add a php.ini file to /wp-admin/ and put these settings in there (assuming your host allows php.ini overrides):
max_input_vars = 3000
suhosin.post.max_vars = 3000
suhosin.request.max_vars = 3000
From: http://anothersysadmin.wordpress.com/2012/02/16/php-5-3-max_input_vars-and-big-forms/
