Object &1 forbidden because of an existing BEFORE EXPORT method

What causes this issue?

Before Export method: The existence of a Before Export method prevents
the object &V1& from being put in BC Sets.
A Before Export method, which runs at the transport release event, has
been defined for this object. As this event does not occur when you put
the data in a BC Set, the Before Export method does not run.
Before Export methods usually check or change tables in the system, for
which the standard transport mechanism is inappropriate or inadequate
for this object.
In most cases you can therefore not use the object in BC Sets, because
the source system can be in an "undefined" status after putting the data
in the BC Set and transporting or activating it (because the Before
Export method has not run).

System Response

You cannot put the object &V1& in BC Sets.

How to fix this error?

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

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.