SAP BF sets should not point to BF sets of customers

What causes this issue?

SAP business function sets should not be changed by modifications in
such a way that they point to business function sets in the customer
namespace.

How to fix this error?

Change the business function set &V1& in such a way that it points to
the business function set &V2&.

Error message extract from SAP system. Copyright SAP SE.