Hi,
The forms which you are having trouble editing are created with a very old version of Form Maker plugin (1.7/2.7 or lower). The structure of the forms has been significantly modified, and these forms will not work with the latest version of the plugin.
However, there is a workaround for this problem. Please install a bit older version of the plugin, e.g. 1.10/2.10. You will afterward be able to edit your forms and recreate them.
Rebuilding the old forms is highly recommended since the new forms will have access to latest features of the plugin. They will also have improved structure and functionality.
Feel free to let me know in case you have questions.
Thank you! Have a wonderful day!
