Message windows disappear off desktop

[Mr B]

Just recently my Outlook 2003 on XP has started exhibiting this very
strange behaviour.

If I click on New Message (or open or reply-to an existing message),
the message window opens but then it immediately zooms off to the
right and off the desktop!
The icon appears on the taskbar but the window can't be moved, and
maximising it makes no difference. Calendar events are OK..

Any ideas how to cure this (or what caused it)?

 

[Mr B]

I just found that if I start Outlook in safe mode then the message
windows display normally.

I tried disabling all the Add-ins under Advanced Options > Add-in
Manager, but that makes no difference.

Any ideas how I fix this?