#Value! error when writing formula - excel

Question

I have a piece of code that loops down a column and inserts a formula into each cell in that column. The code runs, the only problems is that each cell the formula is inserted into displays #Value! Does anyone know how to fix this?
Here is the piece of code with the problem:
Dim j As Long
'Loop down the rows in mainfile
For j = 2 To lastFullRow2
' Make each argument a string, then concatenate it all all into large string
Dim firstArgument As String
firstArgument = "ws_multidax.Range(" & valuecolumnLetter & "2:" & valuecolumnLetter & lastFullRow1 & ")"
Dim secondArgument As String
secondArgument = "ws_multidax.Range(" & parameter1columnLetter & "2:" & parameter1columnLetter & lastFullRow1 & ")"
Dim thirdArgument As String
thirdArgument = "ws_multidax.Range(" & parameter2columnLetter & "2:" & parameter2columnLetter & lastFullRow1 & ")"
Dim fourthArgument As String
fourthArgument = "ws_multidax.Range(" & parameter2columnLetter & "2:" & parameter2columnLetter & lastFullRow1 & ")"
Dim condition3 As String
condition3 = "ws_mainfile.Range(" & "D2:" & D & j & ")"
Dim patid1 As String
patid1 = "ws_multidax.Range(" & "D2:" & D & lastFullRow2 & ")"
With ws_mainfile
Dim commandstring As String
'The formula we want is a concatenated string
commandstring = "{=INDEX(" & firstArgument & ",MATCH(1,(" & secondArgument & "=" & condition1 & ")*(" & thirdArgument & "=" & condition2 & ")*(" & patid1 & "=" & condition3 & "),0))}"
'Insert the formula into each cell as the loop goes down the rows
ws_mainfile.Range("AN" & j).Formula = Eval(commandstring)
'ws_mainfile.Range("AN" & j).Formula = commandstring
End With
Next j
The #Value! gets put into the cells when I run the line with the Eval(commandstring). When I run the line with just formula = commandstring, the formula gets put in each cell, but it does not solve.

Answer 1

Your code has 2 problems:
You are putting in the curly braces of an array formula manually, don't do this
You are putting in an array formula as a regular formula
So to correct, do the following:
'1. Change this line:
commandstring = "{=INDEX(....)}"
'And simply remove the curly braces {} from its beginning and end
commandstring = "=INDEX(....)"
'2. Change this line:
ws_mainfile.Range("AN" & j).Formula = Eval(commandstring)
'To use the .FormulaArray property instead of just .Formula:
ws_mainfile.Range("AN" & j).FormulaArray = commandstring

Answer 2

You're on the right track. There's no need to use the eval function, as you have built a string formula in code. The problem is you have surrounded it with the braces, which excel treats as if you had entered text.
Try this instead:
commandstring = "=INDEX(" & firstArgument & ",MATCH(1,(" & secondArgument & "=" & condition1 & ")*(" & thirdArgument & "=" & condition2 & ")*(" & patid1 & "=" & condition3 & "),0))"
'Insert the formula into each cell as the loop goes down the rows
ws_mainfile.Range("AN" & j).Formula = commandstring