attachments sometimes not displayed

I have a user who has reported problems viewing attachments on sent
items. The recipients of those messages also have problems viewing
the attachments. Sometimes when the messages are opened the
attachments aren't listed in the message header, and therefore cannot
be opened. This happens to both the sender (in Sent Items) and
recipient (in Inbox). Sometimes if they try re-opening the message a
second or even third time then the attachments will be visible in the
header. So it looks as if the attachments aren't being stripped, but
rather that Outlook is having a problem displaying them in the opened
message header, but only sometimes.

All users are running Outlook 2003 SP2 on WIn XP Pro SP2. We are an
Exchange 2003 SP2 shop and the problems have only been reported by
internal users so far. Most of the recipient addresses come from the
GAL in Exchange.

Thanks for any help,
Mike