SAP Message VW660 - Split not possible for shipment &1, deliveries &2

Diagnosis
Splitting the selected deliveries is not possible since the shipment<(>&<)>V1<(>&<)> is connected to the selected deliveries <(>&<)>V2<(>&<)> in a transportation chain. Shipment <(>&<)>V1<(>&<)>, however,was created by an external transportation planning system and can onlybe changed by the same.

System Response
You cannot execute the split for the selected deliveries.

Procedure
Revoke the selection of deliveries <(>&<)>V2<(>&<)> and restart thesplitting process.