Getting Error 400 with VBA in Excel using a working Formula

Question

Im trying to insert multiple Formulas using For loops into my current worksheet. It Crashes everytime with a 400 Error. My Code look slike this:

Sub Generiere_Abteilungs_Zusammenfassung()
    Dim ws, z, s As Integer
    Dim formula As String
    For z = 2 To 3
        For s = 2 To 4
            formula = "SVERWEIS(RUNDEN(MITTELWERT("
            For ws = 1 To (Sheets.Count - 2)
                formula = formula + "SVERWEIS('" + Sheets(ws).Name + "'!" + Cells(z, s).Address + ";Antworten!$B$1:$C$5;2;FALSCH);"
            Next ws
            formula = formula + ");0);Antworten!A1:B5;2;FALSCH)"
            Range(Cells(z, s).Address).Select
            ActiveCell.Formula = "=" + formula
        Next s
    Next z
End Sub

The Formula itself worked when i returned it in a MsgBox and copy and pasted it into excel.