Entry length is incorrect. "&"

What causes this issue?

The key that you entered for the project definition or the WBS element
does not have the same length as was entered in the coding.

System Response

INCLUDE 'NA_ALLG_NOVERARBEITUNG' OBJECT DOKU ID TX

How to fix this error?

Enter the key as it was defined in the coding of the project definition
or WBS element: "&V1&".
INCLUDE 'NA_ALLG_VORGEHEN' OBJECT DOKU ID TX
Check whether the coding for the project definition or the WBS element
were properly maintained on the screen. Make any necessary changes.

Error message extract from SAP system. Copyright SAP SE.