You cannot insert dates in this mode

What causes this issue?

You have selected a mode in project planning board in which you cannot
insert a time bar.

System Response

INCLUDE 'NA_ALLG_NOFUNKTION' OBJECT DOKU ID TX

How to fix this error?

RESET N1
Activate change mode by clicking on the icon with the hand.
Insert the time bar.

Error message extract from SAP system. Copyright SAP SE.