Createmailbox error c1032227 "the obejct is of the wrong class"   

Attempting to create an Exchange 2003 mailbox using ASP, with domain admin 
account, I've got this error message : "The object is of the wrong class 
error id=c1032227 Microsoft CDO for Exchange Management -2147024809"

Technical environment:
Exchange 2003 v6.5.7226.0
Windows 2003 Server Standard Edition SP1
IIS 6
Native 2003 Active Directory environment

This is my code:
Set objuser = 
GetObject("LDAP://xx.yy.com/CN=username,CN=Users,DC=xx,DC=yy,DC=com")
Set objMailbox = objUser 'IMailboxStore interface
objMailbox.CreateMailbox "LDAP://CN=Banque de boîtes aux lettres 1,CN=Banque 
1,CN=InformationStore,CN=EXCHANGESERVER,CN=Servers,CN=EXCHANGESITE,CN=Administrative 
Groups,CN=EXCHANGEORG,CN=Microsoft 
Exchange,CN=Services,CN=Configuration,DC=xx,DC=yy,DC=com"

Help or ideas would be very appreciated.
Regards
Jean

date: Thu, 9 Feb 2006 08:13:03 -0800   author:   Jean Giraud