How to fix Error Runtime 9 when comparing two workbooks - excel

Question

I am trying to create a formula that compares two workbooks.
I get:
Run-time error 9.
Here is the code:
Sub Compare()
Dim wb1 As Workbook
Dim wb2 As Workbook
Set wb1 = Workbooks("Testing1.xlsx")
Set wb2 = Workbooks("Testing2.xlsx")
'Setting variable to represent last row and last column
lRow = Cells(Rows.Count, 1).End(xlUp).Row
lCol = Cells(1, Columns.Count).End(xlToLeft).Column
For i = 2 To lRow
For j = 2 To lCol
'Created the IF then Statement to Highlight Cells that show a difference
If wb2.Sheets("Sheet1").Cells(i, j) <> wb1.Sheets("Sheet1").Cells(i, j) Then
wb2.Sheets("Sheet1").Cells(i, j).Interior.ColorIndex = 5
End If
Next j
Next i
End Sub

Answer 1

Compare the Same Cells in Two Different Workbooks
This is just a basic example that may serve you well at this stage.
Option Explicit
Sub CompareBasic()
' Source: compare; just read
Dim swb As Workbook: Set swb = Workbooks("Testing1.xlsx")
Dim sws As Worksheet: Set sws = swb.Worksheets("Sheet1")
' Destination: compare and highlight
Dim dwb As Workbook: Set dwb = Workbooks("Testing2.xlsx")
Dim dws As Worksheet: Set dws = dwb.Worksheets("Sheet1")
Dim dlRow As Long: dlRow = dws.Cells(dws.Rows.Count, "A").End(xlUp).Row
Dim dlCol As Long
dlCol = dws.Cells(1, dws.Columns.Count).End(xlToLeft).Column
Application.ScreenUpdating = False
Dim r As Long
Dim c As Long
For r = 2 To dlRow
For c = 2 To dlCol
If dws.Cells(r, c).Value <> sws.Cells(r, c).Value Then
' Using 'Color' is preferred for it to work the same,
' not depending on which color palette is used.
dws.Cells(r, c).Interior.Color = vbYellow
Else
' It may have previously been different (highlighted)
' but now it's the same (not highlighted):
dws.Cells(r, c).Interior.Color = xlNone
End If
Next c
Next r
Application.ScreenUpdating = True
MsgBox "Differences highlighted.", vbInformation
End Sub