No network assignment entered for WBS element &

What causes this issue?

When you enter dates in time scheduling, the system creates a network
with these dates in the background. You must enter how the network
should be created in the project profile:
A network for the entire work breakdown structure
A network for each WBS element
In this situation, no assignment has been made for the WBS element &V1&
.

System Response

INCLUDE 'NA_ALLG_NOVERARBEITUNG' OBJECT DOKU ID TX

Error message extract from SAP system. Copyright SAP SE.