Some users in a distribution group receive a blank email sent to that group

We are running Exchange 2003 SP2 on Server 2003 R2 SP2. When a user sends an email to a distribution group some users receive that email with a blank body. This ranges from Outlook 2003 to Outlook 2010. The email also has a blank body in OWA. We use NOD32 as our AV and I was sure that it was an AV thing until I checked OWA. I’ve looked through many forums over the past month with no answers. Any help that anyone could give me would greatly be appreciated.