Ghost user when accepting calendar invite

Our organization has a 2003 Windows Server with Exchange 2003 on it. We have 120 users. I recently deleted a user which is no longer with the organization and all appeared to go fine. Recently, when an invite is sent out to certain people, when they’re accepted, an error returns stating “the e-mail does not exist at this organization” referencing the deleted user. The deleted user is not in the global contact list. I have verified the old address is not in a personal contact file on the involved workstations. I’ve searched all through Active Directory and have had no luck. I’m hoping someone has had a similar situation.

Thans.