Customizing object '&1' cannot be put in a BC Set

What causes this issue?

You cannot put the customizing object '&V1&' in a BC Set. This can be
because:
There is no piece list (tables, from which the data is to be read, must
be specified for each BC Set-relevant customizing object).
The object is not in the system.
The object has a BEFORE-EXPORT method in which tables are only filled
when the data is exported from the system. As the BC Set does not know
this logic, the data is not copied.
The maintenance dialog is based on the table maintenance tools (SM30,
SM34, SM30/SM34 parameter transactions) and manual actions, which fill
tables in the background, run at events.
If it is a view, its definition may be inconsistent:
There are gaps in the key: All key fields must be consecutive at the
beginning of the view.
A key field is a GUID (Global Unique Identifier) or is longer than 255
characters (e.g. a field of data type STRING).
The view is "READ ONLY".
It is explicitly forbidden, for technical reasons.

System Response

No data from object '&V1&' is put in the BC Set. The object itself is
not in the BC Set.
If the object is already in a BC Set, it is removed the next time it is
saved (in the BC Set maintenance transaction SCPR3), or it is ignored by
an activation (in the BC Set activation transaction SCPR20).

How to fix this error?

The transaction SOBJ contains detailed information about the BC
Set-compatibility of the customizing object. The header information for
object '&V1&' contains a BC Set compatibility check pushbutton. If this
check indicates that the object is BC Set-compatible, the person respons
ible for an assigned IMG activity forbid its use explicitly. In this
case, you can check the BC Set-compatibility of the IMG activity in the
IMG (transaction SPRO -> Select activity -> Edit -> Display IMG Activity
-> Check BC Set Compatibility) or the transaction S_CUS_IMG_ACTIVITY,
specifying the technical name &V2&.
For further information, contact your system administrator, the person
responsible for this customizing object, or SAP.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.