Meeting request gets NDR or kickback from Exchange Server

Scenario:

UserA sends a meeting request to UserB and UserA gets a NDR message with the following details:

————————————–

Your message did not reach some or all of the intended recipients.
Subject: test
Sent: 1/24/2008 1:32 PM
The following recipient(s) could not be reached:

—————————————
After digging into Active Directory using ADSIEdit, (which came up empty) I removed all delegates from UserB, added a new delegate that has never been a delegate in UserB’s mailbox, then put the original delgates back for UserB. Basically this resets the delegates and the meeting requests won’t NDR any longer.