Can't open Outlook notes except in a new window

I'm using Outlook 2003 connected to an Exchange Server (part of
SBS2003) at work.

A few months back I noticed that clicking the Notes link on the left
"Navigation Pane" doesn't update the right pane to show my notes... it
just stays on whichever page is already displaying. The Navigation
Pane heading does change to "Notes", but the content doesn't change.

The only way I can now view my notes is to right-click the Navigation
Pane link and select "Open in New Window".

I've put up with this slight inconvenience for a while but now several
colleagues have started reporting similar behaviour.

Does anyone have any idea what I can do to fix this?

Many thanks

James