Object cannot be created at this URL because an object named by thisURL already exists

[Dhananjay]

Hi All,
I want to develop one application in vb.net for exchange 2000.

I tried to add one contact with the code snippet below. The same logic
is there for appointment on Microsoft's site.
(I added Microsoft CDO exchange library for 2000 & activex data object
2.5 reference to the project)

Dim sURL As String
sURL = "http://sbsserver/Exchange/trial/contacts"

Dim oCn As ADODB.Connectio n = New ADODB.Connectio n()
' For server change oCn.Provider to "exoledb.dataso urce";
oCn.Provider = "exoledb.dataso urce"

oCn.Open(sURL, "", "", 0)
If oCn.State = 1 Then
Console.WriteLi ne("Good Connection")
Else
Console.WriteLi ne("Bad Connection")
Return
End If

Dim iConfg As CDO.Configurati on = New CDO.Configurati on()
Dim oFields As ADODB.Fields

oFields = iConfg.Fields
oFields.Item(CD O.CdoCalendar.c doTimeZoneIDURN ).Value =
CDO.CdoTimeZone Id.cdoPacific
' TODO: Set Meeting Organizer
oFields.Item(CD O.CdoConfigurat ion.cdoSendEmai lAddress).Value =
"or*******@exam ple.com"
oFields.Update( )

' Below is my code in which I just removed the logic of creation of
appointment with creation of contact

Dim oContact As New CDO.Person
' *************** *************** *********
oContact.FirstN ame = "FirstTrial "
oContact.LastNa me = "LastTrial"
oContact.Config uration = iConfg

oContact.DataSo urce.SaveTo sURL, , _
ADODB.ConnectMo deEnum.adModeRe adWrite, _
ADODB.RecordCre ateOptionsEnum. adCreateNonColl ection, _
ADODB.RecordOpe nOptionsEnum.ad OpenSource, _
"", ""
oContact = Nothing

oCn.Close()
oCn = Nothing
oFields = Nothing
' *************** *************** *********

Now here if I run the program for first time, my contact is
successfully get created in the trial's contacts folder. But if I run
this program second time, it gives me error "Object cannot be created
at this URL because an object named by this URL already exists". On
some forum, the solution to error is given as - Try to create the
contact with readWrite & Overwrite attribs. So I changed the above
creation code from
"ADODB.RecordCr eateOptionsEnum .adCreateNonCol lection" to
"ADODB.RecordCr eateOptionsEnum .adCreateOverwr ite". But it gives me the
error as "Unspecifie d error". So how I can create a contact or modify
existing contact in the trial's mailbox?
Further how I can create the task for Trial using similar code above?
Also please anyone point me to the right direction where I can get the
knowledge about step by step exchange programming on the internet?

Thanks in advance