New entry not possible because of GTABKEY registration

What causes this issue?

The first entity cannot be inserted because it is a clone of the second
entity with just another name. Because of the actual
GTABKEY-registrations the first entity must have the same internal key
as the second entity.
For example:
You create a model named A in system 1 which then automatically gets the
internal key 123. The combination (123,A) is stored in table GTABKEY.
Then you create the same model A in system 2 which also gets internal
key 123.
After that you rename model A in system 2 to B. Now you have model B in
system 2 with internal key 123.
Finally you try to create a model A in system 2 again. This model must
get internal key 123 because of the GTABKEY-registration (123,A) -
because it is the same model as model A in system 1 - and thus model A
and model B in system 2 are in fact the same model.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

You cannot create entity 1. Modify entity 2 instead.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.