Need help to create Excel macro for Outlook Reminder

Hi,

I'm no developper and I try to create a macro in Excel 2003 to create an Outlook Reminder for an user to update a workbook on a periodical basis (determined according to a value in the workbook). I have been able to figure the following coding:

Sub CreateAppointment()
Dim olapp As Outlook.Application
Dim olappItem As Outlook.AppointmentItem

Set olapp = GetObject("", "Outlook.Application")
Set olappItem = olapp.CreateItem(olAppointmentItem)
With olappItem
.Start = Range("'Out_App'!A6").Value
.Subject = Range("'Out_App'!B6").Value
.Duration = 1
.ReminderSet = True
.Save
End With
End Sub

However, when I run the macro, I receive the following error message: "User-Defined Type Not Defined" and nothing happens.

Could you please help me with this task?

Thanks

Eric