I just installed this on a client's site, and when I try to edit the Options and click the "Update Settings" button, I get taken to the standard WP "Page Not Found" page and the settings don't save. The URL in the address bar is: https://www.DOMAIN/wp-admin/options-general.php?page=wpmem-settings&tab=options.
The other tabs update just fine (fields, dialogs, emails). I've tried turning off the other plugins and using one of the standard WP themes. I've also tried installing the plugin using the automatic updater and manually via FTP.