SAP Message B1874 - You cannot modify the hierarchy. Refer to the long text.

Diagnosis For the BAPI (&v1&, &v2&) the indicator "release" for the associatedIDoc type &v3& of the generated ALE/IDoc interface is active. You can assume that the ALE/IDoc interface has already been delivered.The dependencies of the BAPI table parameters can no longer be changedas this would affect downward compatibility. Procedure Due to compatibility problems a new BAPI with the new BAPI tableparameter hierarchy must be created. Then the ALE/IDoc interface mustalso be generated. This measure is also necessary when only one optional table parameteris added to the BAPI. If these optional table parameters affect thehierarchy, the BAPI has been modified incompatibly to all itspredecessors.