Wo ist hier der Fehler?

Sub test()
Dim a As Long
Dim rng_a As Range
Dim ZElle As Object
Dim str_formulaOld As String
Dim str_FormulaNew As String
Dim str_formulaNew_Part1 As String
Application.Calculation = xlCalculationManual
For a = 1 To ActiveWorkbook.Worksheets.Count
Set rng_a = ActiveWorkbook.Worksheets(a).UsedRange
For Each ZElle In rng_a
If ZElle.HasFormula = True And Left(ZElle.Formula, 15) = "='Q:\SC\S C A\1" Then
str_formulaOld = ZElle.Formula
str_formulaNew_Part1 = Mid(str_formulaOld, 2, Application.WorksheetFunction.Find("-'Q", str_formulaOld, 1) - 2)
str_FormulaNew = "=wenn(abs((" & Mid(str_formulaOld, 2, Len(str_formulaOld)) & ")/" & str_formulaNew_Part1 & _
"))<0,1;"""";" & Mid(str_formulaOld, 2, Len(str_formulaOld)) & ")"
ZElle.Formula = str_FormulaNew
End If
Next
Next a
Set rng_a = Nothing
Application.Calculation = xlCalculationAutomatic
Application.Calculate
End Sub