One day it's fine; Next Morning the Dam Breaks

I have 2 servers, one running Server 2003, the other SBS 2003 both standard
edition. Outlook 2003 came with the SBS 2003, and I installed it on the
client computers.

Everything has been going good, then just this morning, the CEO can't get to
his contacts...

He would click on New Message, then click on the "To" button to bring up the
address book, and it has an error message, saying that it can't open up the
address book for this mailbox. It has either been moved or deleted. or you
don't have permission to access this.

I click on the OK button, and the address book comes up BLANK. Then up in
the upper right corner of the address book "Show names from the:" there is
the Outlook Address Book, then underneath that slightly indented, Contacts
and right underneath that same margins, Contacts again, and in that contacts
is his address book with all the names and everything.

Why did this change? How can I change it back?