In an Exchange Server 2010 environment Outlook 2003 users may receive an error message when they attempt to connect to an Exchange 2010 Mailbox server.
Your Exchange Server administrator has blocked the version of Outlook that you are using. Contact your administrator for assistance.
This error will occur if there are no Public Folder databases in the Exchange Server 2010 organization.
You can resolve the error by provisioning at least one Public Folder database on an Exchange 2010 Mailbox server.