Worksheetfunction.match arguments causing function to fail

Try like this…

Dim vResult As Variant

For i = 1 To UBound(MyConcat)
    vResult = Application.Match(Range("AG" & (20 + i)), Range("AN21:AN" & LastRow), 0)
    If IsNumeric(vResult) Then
        ResultArray(arraycounter) = MyConcat(i, 1)
        arraycounter = arraycounter + 1
    End If
Next i