error when hiding application while another document open

Hi

I am getting error when I hide application in document open event and show userform
error : you cannot close microsoft word because a dialog is open
note the error only appear when second word file is open but no dialog is open
any idea to avoid this error?
I stop application alert but still, and I sendkey enter once userform load but still

Private Sub Document_Open()
Application.DisplayAlerts = wdAlertsNone
Application.Visible = False
UserForm1.Show
End Sub