Sub Insert_IfIsError()
'Written by Barrie Davidson
Dim Orig_formula As String
Dim formulaRg As Range
Dim formcell As Range

With Application
    .ScreenUpdating = False
    .Calculation = xlCalculationManual
End With

For Each formcell In Selection
Orig_formula = formcell.Formula
Orig_formula = "=IFERROR(" & Mid(Orig_formula, 2, Len(Orig_formula) - 1) & ","0")"
formcell.Formula = Orig_formula
formcell.HorizontalAlignment = xlRight
Next

With Application
    .ScreenUpdating = True
    .Calculation = xlCalculationAutomatic
End With

End Sub