I forget about this every time and have to search the net again for the info: since Outlook 2000 there have been certain file types that can’t be opened or saved by default when they arrive attached to an email. If such attachments are encountered, Outlook shows the following message: “Outlook blocked access to the following potentially unsafe attachments”. Everything you need to know to change this is on this Microsoft KB page, and it even works with Outlook 2007.