Network type "&" does not exist

What causes this issue?

Network type &V1& either:
does not exist or
was not entered in the network profile
In either case, you cannot create activities.

System Response

INCLUDE 'NA_ALLG_NOVERARBEITUNG' OBJECT DOKU ID TX

How to fix this error?

INCLUDE 'NA_ALLG_MOEGLICH' OBJECT DOKU ID TX
RESET N1
Check your entries.
If necessary define the network type in Customizing the Project System
If necessary, enter a network type in the network profile.
You can also maintain the network type in scheduling using the menu
option <zh>Settings</>.

Error message extract from SAP system. Copyright SAP SE.