Why is the Send method not working on VBA project?

I'm trying to send mails using VBA code. We deleted the display method but it is still not working.

It displays the email with every property of the object Correo, but it's not sending.

It raises error 438.

Sub sendmail(propietario As String, activo As String, departamento As String)

    Dim OutApp As Object
    Dim Correo As Object

    With Application
        .EnableEvents = False
        .ScreenUpdating = False
    End With

    On Error Resume Next
    Set OutApp = GetObject("", "Outlook.Application")
    Err.Clear
    If OutApp Is Nothing Then Set OutApp = CreateObject("Outlook.Application")
    OutApp.Visible = True
    Set Correo = OutApp.CreateItemFromTemplate("C:\Users\plantilla.oft")

    With Correo
        .To = propietario
        .CC = "mail@gmail.com"
        .Subject = "[Recertificación de Usuarios] " & activo & " - " & departamento
        .Attachments.Add "C:\Users\hello.xlsx"
        Set .SendUsingAccount = OutApp.Session.Accounts.Item(1)
        .Display
        .Send
    End With

    With Application
        .EnableEvents = True
        .ScreenUpdating = True
    End With

    Set Correo = Nothing
    Set OutApp = Nothing

End Sub