Please help urgently!!!!!!datediff in vb.net

[kenone]

Am working with vb.net and Sql Server2000.on my program has to calculate the difference between two dates ,the result should be in months.ie RETIREDATE - HIREDDATE=number of months served.Surprisingly ,am getting ZERO months as a result.below is my code;

Public Overloads Function DateDiff( _
        ByVal Interval As DateInterval, _
        ByVal Date1 As Date, _
        ByVal Date2 As Date) As Integer

Private Sub DateTimePicker3_ValueChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DateTimePicker3.ValueChanged
        Dim service As integer
        service = DateDiff(DateInterval.Month, DateTimePicker3.Value,  CDate(txtRetireDate.Text))
        txtService.Text = service.ToString
    End Sub

I am suspecting that the final statement (txtService.Text = service.ToString)might be the problem???
noteatetimepicker3 holds DATEHIRED.
Please help this urgently.!!!!!.I have been trying to figure it out in several ways to no avail.
I hope I will get a helpful support.thanks