Vlookup function assistance needed in VB script, using String for most recent sheet

my VB script obtains the sheet name of the most recent sheet in the workbook, storing the sheet name as a string, however when I reference this string in a Vlookup function, Excel cannot locate the sheet. The sheet name is in date format, so the most recent sheet is yesterday's date (in Australian date format), '08-06-2021'. The macro runs, but when it comes to running the VLookup function, it cannot find the sheet and interestingly the following message appears:

Cannot find "2021". Copy from:

And opens a window to locate the Spreadsheet, and then select the Worksheet within the spreadsheet. For fun I renamed the '08-06-2021' sheet to just '2021' to see if that would work. This also didn't work, and the error was even more unusual, as it is now trying to locate a sheet name that doesn't exist. The new message was:

Cannot find "C1322021". Copy from:

As mentioned, there is no sheet with the name C1322021. Here is the relevant VB code:

Dim wsData1 As Worksheet  
Dim Firstrow As Long
Dim Lastrow As Long
Dim Lrow As Long
Dim rWorkSheet As String

Dim i 

  i = ActiveWorkbook.Sheets.Count - 1
  rWorkSheet = Worksheets(i).Name

  Firstrow = .UsedRange.Cells(1).Row + 1
  Lastrow = .UsedRange.Rows(.UsedRange.Rows.Count).Row

       For Lrow = Lastrow To Firstrow Step -1
       With ActiveSheet.Cells(Lrow, "M")

            sNotes = "=VLookup(C" & Lrow & rWorkSheet & "!C:N, 12, False)"

                ActiveSheet.Cells(Lrow, "M") = sNotes

        End With

Appreciate any assistance with this, as it has me stumped!

TIA,

Michael