Auto insert of Username in a set cell

Good evening happy campers,

I have a workbook with 4 tabs.

On the tab named 'Requests' i want excel to automatically insert my windows login name into cell A1 on the requests tab as soon as i open the workbook.
And at present it's killing me lol
So far i have the following -

Private Sub Workbook_Open()
Sheets("Requests").Range("A1") = Application.UserName
End Sub

But this does not work

Thanks in advance, galvinpaddy.