Deleted Field (no duplicate) stops data entry save

Deleted Field (no duplicate) stops data entry save

For ACA Materials Management Application
Form Name: Curriculum Entry Form
Originally a field called "key 2" was added to the form with the No Duplicate selected. Later I decided not to use the field as a foreign key and deleted the field. At first it wasn't a problem. Now the field seems to have returned and results in the following message.
1. [t_38790000000003025] null, message from server: "Duplicate entry '0' for key 2".

The field can't be seen or accessed in the application.
robertsouth2