Read receipts causing outlook to crash

Good afternoon all,
I've got a bit of a strage one..
One of my users receives an e-mail from an external source on a fairly regular basis, the external source always requests read receipts.
If my user clicks 'no' then the outlook process closes instantly. It's only for the one external source that the issue lies - I've tried with other external sources and internal mails from within exchange and it's fine.
If he chooses yes there is also no issue.
If anybody can shed any light on this it'd be appreciated!
Exchange 2003 - Outlook 2003 - OS: XPSP2
Mailmarshall / Blackspider