Run time error 3078 (1 Viewer)

Hello everyone, hope everything is good!

I have this code
Private Sub Vertragsnummer_AfterUpdate()
Dim NewVertragsnummer As String
Dim stlinkcriteria As String
NewVertragsnummer = Me.Vertragsnummer.Value
stlinkcriteria = "[NewVertragsnummer] = " & "'" & NewVertragsnummer & "'"
If Me.Vertragsnummer = DLookup("[Vertragsnummer]", "Tbl_Dokumentation", stlinkcriteria) Then

MsgBox "The Contract Number," & NewVertragsnummer & ", Already exists!!" _
& vbCr & vbCr & "Please Check The Contract Number Again.", vbInformation, "duplicate information"

Me.Undo
End If

End Sub
I’m trying to avoid duplication inside my database but it keeps telling me that “tbl_dokumentation” does not exist! Although i have it.
Also for my form the data source is also the table documentation.

If you are trying to pull value from field Vertragsnummer, why does criteria reference field [NewVertragsnummer]? Is there really a field by that name?

If you want to provide db for analysis, follow instructions at bottom of my post.

I got to be honest with you i was following the steps of a video, i’m still a beginner!
And no there’s no field with the name newVertragsnummer? I’m not really what I’m supposed to put in the criteria reference field!
Btw thanks for the fast reply!

Thank you i just solved the problem now!