Areas must have unique names. Operation not performed

What causes this issue?

You are editing a subscreen or a table control and want to assign a
field name to it or change the existing field name. However, the screen
already contains a subscreen or table control with this name.

System Response

The system identifies table controls and subscreens by their field
names which must be unique. For this reason, it rejects the new field
name.

How to fix this error?

Choose a different field name.

Error message extract from SAP system. Copyright SAP SE.