Outlook Mail notification envelope

[Trevor <trs55@xxxxxxxxxxx>]

I am getting an annoying problem with Microsoft Outlook 2003,
sometimes when I receive an email the notification envelope sits in
the task-bar till I read it as it should, but on other occasions it
justs flashes up on the task-bar and then goes again, not a problem if
I am using the computer at the time as I hear the audible
notification. I have checked the settings and the "Show envelope in
notification area" button is still ticked so I am at a loss as what to
do next, or just put up with it. Any advice would be appreciated.
Trevor Smith