I have a user that says that a couple of weeks ago, when they composed Email
messages, they would type in the beginning of someone's Email address, and it
would auto-complete for them without any problem.  Now, when they go to type
in an address, all of the suggested addresses that appeared before are no
longer displaying.  

This user has not changed their machine, and they have not recreated their
profile either, so I wondered if it's possible that their account in Outlook
might be referencing another nickname file, or is it possible the contents of
the nickname file might have been cleaned out?  Also, is it possible the an
old nickname file may be cached elsewhere?

I know this is a weird question, but it doesn't make sense to me how
suggested nicknames could be there one second, and then be gone the next.