Invitations and Blank Address List
This is a solution submitted by an IT contractor for one of our firms:
"Apparently the Exchange Server had some missing settings. In the Exchange Management Console, under Organization Configuration and selecting Mailbox, there's a tab called "Database Management" and by going into the "Properties" of the Mailbox Database listed under that Tab, there is a section where the client settings of the Offline Address Book was empty. I selected the Default Offline Address Book and restarted the Client PC's and that solved the problem. If it didn't I had them download the offline addressbook under the Send Recieve tab. Just thought I'd update you in case anyone else had the issue."