I am happy I found this thread. I was really scratching my head about this error and it would have probably taken me ages to find out that Restrict Content is the reason for it.
I have the same or similar problem, it happens when a script (from a plugin I am working on) inserts a post in a custom post type.
WP_DEBUG is enabled, shows the same error message as Chrislancs gets.
Notice: Undefined index: rcMetaNonce in […]/wp-content/plugins/restrict-content/includes/metabox.php on line 85
The problems gets “worse” when trying to delete the post. After clicking on the “Trash” link, I get a white page saying:
Notice: Undefined index: rcMetaNonce in […]/wp-content/plugins/restrict-content/includes/metabox.php on line 85
Warning: Cannot modify header information – headers already sent by (output started at […]/wp-content/plugins/restrict-content/includes/metabox.php:85) in […]/wp-includes/pluggable.php on line 1228
As stated by Chrislancs, the problem goes away when deactivating the plugin.
I guess the code that handles the “rcMetaNonce” post_meta entry needs to be revised.
