VLOOKUP from another spreadsheet using VBA - excel

Question

I have a master spreadsheet that analyzes records from another spreadsheet with rows going all the way up to 1.4 million.
Below are the relevant pieces from the code:
Sub Whyamidoingthis()
Dim USISINLfp As String
Dim ISINL As String
Dim echeck As String
Dim wUSISIN As Workbook
Dim lastrow As Long
Dim Result As Worksheet
Dim i As Long
Set OutShVar = ThisWorkbook.Worksheets("in1")
ISINL = "CONSOLIDATED - Country_Of_Incorp_US_2019-03-01 (Consolidated).xlsx"
USISINLfp = "W:\Product Platforms\ISIN- CUSIP Country of Incorporation\March 2019\"
Workbooks.Open (USISINLfp & ISINL)
Set wUSISIN = Workbooks(ISINL)
With Result
lastrow = .Cells(.Rows.Count, "H").End(xlUp).Row
End With
'US Security 1
For i = 2 To lastrow
With Result
echeck = Trim(.Range("O" & i))
If echeck = "" Then
.Range("P" & i & ":Q" & i).Value = "N"
Else
.Range("P" & i).Value = "=ifna(vlookup(O" & i & "," & ISINL & "First Sheet'!$B:$C,2,false)," & Chr(34) & "N" & Chr(34) & ")"
.Range("Q" & i).Value = "=ifna(vlookup(O" & i & "," & ISINL & "Second Sheet'!$B:$C,2,false)," & Chr(34) & "N" & Chr(34) & ")"
'Debug.Print "=ifna(vlookup(O" & i & "," & ISINL & "Second Sheet'!$B:$C,2,0)," & Chr(34) & "N" & Chr(34) & ")"
End If
'US Security 2
echeck = Trim(.Range("S" & i))
If echeck = "" Then
.Range("T" & i & ":U" & i).Value = "N"
Else
.Range("T" & i).Value = "=ifna(vlookup(S" & i & "," & ISINL & "First Sheet'!$A:$C,3,false)," & Chr(34) & "N" & Chr(34) & ")"
.Range("U" & i).Value = "=ifna(vlookup(S" & i & "," & ISINL & "Second Sheet'!$A:$C,3,false)," & Chr(34) & "N" & Chr(34) & ")"
End If
End With
Next I
If Not wUSISIN Is Nothing Then wUSISIN.Close savechanges:=False
End Sub
The code is getting stuck at the following line:
.Range("T" & i).Value = "=ifna(vlookup(S" & i & "," & ISINL & "First Sheet'!$A:$C,3,false)," & Chr(34) & "N" & Chr(34) & ")"
Whenever a result is found and the error is application defined error.

Answer 1

Try this formula:
"=ifna(vlookup(O" & i & ",'[" & ISINL & "]First Sheet'!$B:$C,2,false)," & Chr(34) & "N" & Chr(34) & ")"
This places square brackets around the workbook name and single quotes around the workbook-worksheet combo. See this tutorial about using VLOOKUP from another workbook.