Inserting formula using VBA in Excel does not work - vba

Question

First of all, I have tried to look at all the other examples of adding a formula using VBA, and I think I have tried to apply all the answers in this code
Sub AddFormulas(SheetName As String)
Dim i As Integer
'Switch worksheet
Set Wksht = ThisWorkbook.Worksheets(SheetName)
Wksht.Activate
Application.Calculation = xlCalculationManual
i = 2
While Not IsEmpty(Cells(i, 1))
Wksht.Cells(i, 18).Formula = "=IFERROR(VLOOKUP(A" & i & ";" & Wksht.Cells(1, 18) & "!$A:$A;1;FALSE);" & Chr(34) & "MISSING" & Chr(34) & ")"
i = i + 1
Wend
Application.Calculation = xlCalculationAutomatic
End Sub
But still, it gives me this anoying error, that I can't interpret
If I change my line to
Wksht.Cells(i, 18) = "'IFERROR(VLOOKUP(A" & i & ";" & Wksht.Cells(1, 18) & "!$A:$A;1;FALSE);" & Chr(34) & "MISSING" & Chr(34) & ")"
Then I get no error, and the correct formula is added, although as a text string
What is wrong, since it would not add what to me looks like a valid formula?
//V

Answer 1

The Formula property requires formulas to be written in English, i.e. English function names (not an issue here) and commas as separators rather than semi-colons.
So your statement should be:
Wksht.Cells(i, 18).Formula = "=IFERROR(VLOOKUP(A" & i & "," & Wksht.Cells(1, 18) & "!$A:$A,1,FALSE)," & Chr(34) & "MISSING" & Chr(34) & ")"
If you don't mind having "portability" issues, you could also use the FormulaLocal property, i.e.
Wksht.Cells(i, 18).FormulaLocal = "=IFERROR(VLOOKUP(A" & i & ";" & Wksht.Cells(1, 18) & "!$A:$A;1;FALSE);" & Chr(34) & "MISSING" & Chr(34) & ")"

Answer 2

Write the formula as it should be in Excel, select it and run the following code:
Public Sub PrintMeUsefulFormula()
Dim strFormula As String
Dim strParenth As String
strParenth = """"
strFormula = Selection.Formula
strFormula = Replace(strFormula, """", """""")
strFormula = strParenth & strFormula & strParenth
Debug.Print strFormula
End Sub
It should print it as it should be.

Answer 3

I believe your code is giving error becouse of this Wksht.Cells(1, 18) part of line in this row Wksht.Cells(i, 18).Formula = "=IFERROR(VLOOKUP(A" & i & ";" & Wksht.Cells(1, 18) & "!$A:$A;1;FALSE);" & Chr(34) & "MISSING" & Chr(34) & ")". Make sure that Wksht.Cells(1, 18) really contains name of worksheet your are trying to address. If this cell is blank, you will receive previously mentioned error.