Production orders already exist for the grouping WBS element

What causes this issue?

There are already production orders in the system, wioth which material
is being produced for the individual stock of the grouping WBS element.

System Response

INCLUDE 'NA_ALLG_NOVERARBEITUNG' OBJECT DOKU ID TX

How to fix this error?

Check the change to the MRP type or the account assignment of the
existing production orders for this WBS element.

Error message extract from SAP system. Copyright SAP SE.