Are you able to check to see if there are any errors being logged when you get that error? If you have WP_DEBUG
enabled in your wp-config.php file you can find this on your sever at wp-content/debug.log and then look for any reference to “sign-up-sheet”. If you find an error logged at the same time you tested editing in the admin and it failed, then can you please send me the exact error you are seeing?
It might also be helpful if you can please confirm which versions you are running of the following… WordPress, Sign-up Sheets Pro Plugin, and PHP. If it is easier, you can send us a copy of your “System Information” which is found under Sign-up Sheets > Help in your admin. You can post it as a reply in this form and just make sure to check the “Set as private reply” before submitting. Or if you prefer, you can send it through out Contact Form.