No reference location defined --> data transfer not possible

What causes this issue?

You have tried to change the data origin of this field by specifying
that the field data is to be copied from the
<GL:reference_functional_location>reference functional location</>.
This is not possible, as this <GL:functional_location>functional
location</> does not have a reference location.

System Response

INCLUDE 'KEINE-VERARBEITUNG' OBJECT DOKU ID TX LANGUAGE E

How to fix this error?

In this particular case, the only method of allowing data to be copied
from a reference functional location to this particular functional
location is by allocating it a reference location. Before you do this,
however, you should think carefully about the consequences.

Error message extract from SAP system. Copyright SAP SE.