WBS element & does not exist

What causes this issue?

WBS element &V1& does not exist.

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

System Response

INCLUDE 'NA_ALLG_NOVERARBEITUNG' OBJECT DOKU ID TX

How to fix this error?

Check to make sure that you maintained the right key for the WBS element
Change it, if necessary.

Error message extract from SAP system. Copyright SAP SE.