how to add a date when opening up the worksheet

one question for winon, when i set the workbook_open in the ThisWorkbook, the macro fails on the B1 line. thoughts?

Private Sub Workbook_Open()
    
    If MsgBox("Should the date be updated at this time ? ", vbCritical + vbYesNo, ("Confirmation Required")) = vbYes Then
    Range("B1").Value = Range("B1").Value + 7
    Else: Range("B1").Value = Range("B1").Value
    Exit Sub
    End If

End Sub

the error is "run time error 1004, method range of object _Global failed