how many calendars do you have on the list? how many folders are in each nav
bar module? (tasks, contacts etc, but just Favorite Folder in Mail - not the
entire folder list seen in the folder tree) There is a limit, I forget what
it is offhand, only that it's high enough that the average user won't ever
hit it. You can check id it's this by removing one calendar that sticks and
replacing it with one of the two that doesn't stick. If the folder sticks,
you have too many in your nav pane. If it doesn't and the one you removed is
back, then outlook isn't closing cleanly and the Nav bar file isn't getting
saved. It's also possible the nav bar file is corrupt - the fix is to delete
it and make a new one. If you have a lot of folders on it, it's a chore.
If neither of these reasons seem to the cause, does your organization have
more than one exchange server and are the two partners on the same exchange
server you are?