Variant &1 cannot be a component of prepack material &2

What causes this issue?

Variant &V1& cannot be a prepack components. Some possible reasons are:
The variant &V1& has an empties BOM (bill of materials)
The variant has a material type that is not valid for BOM items

System Response

The prepack material can no longer be released.

How to fix this error?

Remove the component from the prepack material.

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.