This error message is displayed when you have selected a Form for a question in your Table (Subform), and you have used that Form in a given Level more than once.
- The selected Form is used as a Subform more than once in the same Level.
- The Subform is also being used as a standalone Form elsewhere in your workflow.
A Form can only be used once in any given Level, including Subforms.
If you see the same error message but you don't use Table (Subforms) in your Project, see this article: