Odd Changes in Outlook Contacts File.

Ok, Experts; Here's a good one for you.  

I have a client with a contacts file with about 1200 entries in it. The Environment is Microsoft Small Business Server 2003, using exchange for email. This one particular Contacts list has changed overnight, for no APPARENT reason. Here are some of the anomolies:

A number of the contacts have simply disappeared.

A number of the contacts have reverted to older email addresses, phone numbers, etc, but not all.

While some of the contacts have changed to older information, some of the newer contacts that have been added days ago remain the same.

It's kind of like a Ghost is changing information.

There COULD be a "human error" element to this, but the facts would not indicate that.

Any thoughts, or should I just call an Exorcist.......

500 points, this is a weird one......AND urgent......