Conflict with WPnewsman plugin

I’ve discovered a conflict between All-In-One and the plugin WPnewsman (https://wordpress.org/plugins/wpnewsman-newsletters/). I’m unable to save changes to templates in the plugin when All-In-One is activated. WPnewsman works fine when I deactivate All-In-One. WPnewsman support responded to deactivate one setting at a time and then leave deactivated. So far I have been unable to find the exact setting. Any suggestions on what All-In-One setting would effect the ability to edit and save templates in another plugin?

Thanks again, Mike

https://wordpress.org/plugins/all-in-one-wp-security-and-firewall/