Symptoms

Line 121Cannot insert duplicate key row in object 'Form.ActionItem_Design' with unique index 'UX_Form_ActionItem_Design_ID'

 

Diagnoses

Client cannot check out a form.
Receiving an error
Line 121Cannot insert duplicate key row in object 'Form.ActionItem_Design' with unique index 'UX_Form_ActionItem_Design_ID'

 

Resolution

The error was being caused by another form being checked out.
This other form was used as a subform on the form that was having the problem.
Checking out then checking in all forms/views that are referenced by this form then checking this one out should resolve the issue