I have created a form on a list. I deleted the form as I no longer need it. The issue is that when I try to edit an item in the list, it tries to open the Nintex Form and fails. How do I reset the list to use standard SharePoint?
Here is a site that evoke same error you got, I hope that it will help you!
Unable to find the default new or edit form for list in SharePoint.
Did you try to re-create the Nintex form and then delete it again?
Retrieving data ...