Change number & does not allow you to change BOMs

What causes this issue?

You want to use change number &V1& to change a BOM or to create a
variant for an existing BOM. However, this change number does not allow
changes to BOMs.
One of the following situations triggered this error message:
In the change master, the corresponding object type (eg. BOM,
routing/plan) is not active, so it is not possible to create or change
objects with this object type using this change number.
The corresponding object type is currently locked for the creation of
new data or changes.
Change number &V1& is the number of an ECR. In this case, an object
management record is required for the BOM. However, no object management
records exist for the selected ECR.

How to fix this error?

Check your entries.
If you really want to create your variant or make your changes using
this change number, consult your system manager responsible for change
master records to get the change number adapted to suit.

Error message extract from SAP system. Copyright SAP SE.