I'd been getting PHP 'notices' to the effect of:
"Notice: has_cap was called with an argument that is deprecated since version 2.0! Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /Users/***/wordpress/wp-includes/functions.php on line 3466"
This message was frustrating as it seemed to interfering with modification of the headers.
ie. After pressing 'save' on the 'Edit User' page, I was presented with the previous notice, plus the following warning:
Warning: Cannot modify header information - headers already sent by (output started at /Users/***/wordpress/wp-includes/functions.php:3466) in /Users/***/wordpress/wp-includes/pluggable.php on line 934
And the rest of the page content was not displayed.
So after a bit of searching I found that in cache-images.php, line 86, the function call 'add_management_page' contained the argument that is deprecated.
I changed it from:
add_management_page( __( 'Cache Remote Images', 'cache-images' ), __( 'Cache Remote Images', 'cache-images' ), 8, __FILE__, 'mm_ci_manage_page' );
add_management_page( __( 'Cache Remote Images', 'cache-images' ), __( 'Cache Remote Images', 'cache-images' ), 'activate_plugins', __FILE__, 'mm_ci_manage_page' );
Now the notice is gone, and the headers are not modified.
The question is; is this the correct fix?
Also, is the capability level of 'activate_plugins' a suitable one?