Find & Replace on Workbook Open - Error Method 'Cells' of object'_Global' failed

Hi,

I recorded a macro to be used on Workbook Open which finds and replaces blank looking cells to truly make them blank. However, I keep getting the following error:

Run-time error '1004':
Method 'Cells' of object '_Global' failed

Does anyone know what the issue is with my code & what a possible solution might be?

Option Explicit
Private Sub Workbook_Open()

 Application.ScreenUpdating = False

    ActiveSheet.Cells.Find(What:="", After:=ActiveCell, LookIn:=xlFormulas, LookAt:= _
        xlWhole, SearchOrder:=xlByRows, SearchDirection:=xlNext, MatchCase:=False _
        , SearchFormat:=False).Activate
  
    ActiveSheet.Cells.Replace What:="", Replacement:="------", LookAt:=xlWhole, _
        SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, _
        ReplaceFormat:=False

    ActiveSheet.Cells.Replace What:="------", Replacement:="", LookAt:=xlWhole, _
        SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, _
        ReplaceFormat:=False

Application.ScreenUpdating = True

End Sub

Thanks for any help on this!