Outlook-subfolders in folderlist are closed on startup

[Henrik]

Hello,
one of our users has the problem, that sometimes
subfolders in the folderlist are closed after
outlookstartup.

This problem happens when he is opening outlook the first
time in the morning.
During the day all folders are open as they where before
closing.
First i thouth, it depends on the single-mailbox-backup,
which runs each night, but i tried it with another mailbox
and all was working right.
Does anybody have an idea ?

We are using OL 2000 with Exchange 5.5 SP4

Thanks

Henrik