That error message will only show if WordPress returns an error when trying to add the sheet to the database table. So, sounds like you have an issue with your database.
Have you used the plugin previously and been able to add sheets? Or just now trying it for the first time?
Try deactivating and then reactivating the plugin to ensure that any database updates have been properly applied (some new fields were added to the database tables in different versions).
Other than that, without seeing some kind of database error log or some other SQL debug info, it’s hard for me to know what is going on. Plugin works just fine here (just added a sheet) with latest versions of everything, and nobody else is reporting any issues. Also, since that is an error that is returned by the WordPress wpdb->update method, it means that WordPress is getting some kind of error when it tries to update the database.
Thanks for your response. We are first time users for this plugin. Tried deactivating and reactivating as you suggested, but sadly to no avail.
We had a plugin author offer assistance with his plugin a while back and are finding that he corrupted some of our code among other things. Could be that your plugin might not work for us with whatever that guy did.