This message will be displayed in Hierarchical Data Extraction (HDE) Levels, in a parent/child Form scenario where another reviewer (User B) has opened a new instance of any repeating Subform for the reference in question, and you (User A) try to edit responses afterward.
This can be confirmed by gathering the RefID(s) in question and running a report in Datarama, In Advanced Options, select "Show all versions of form data" and deselect "merge sets by key."
In the Datarama output, look for instances where User A is listed as a "User" and User B is a "Revision User". User B added a Subform, subsequently User A tried to edit the Subform and got the error message.
To enable editing, it is recommended that the Admin assign the "Audit Responses" permission for User A in the DistillerSR Permission Matrix.