Automatic module generation determined -> manual creation not possible

What causes this issue?

At least one subsequent processing step was successfully carried out
and saved for this promotion. The system determined that modules and
plant group assignments are to be generated automatically. They are
generated via Listing. Other subsequent processing functions only
determine the modules and plant group assignments. This is necessary so
that plant-to-material assignments are the same for all follow-on
processing functions.

System Response

Manual modules can no longer be created.

Error message extract from SAP system. Copyright SAP SE.