attached email messages

i am using Microsoft Outlook 2003 to have my ISP email go into. i am not sure when this started to happen but when someone sends me an email message with an email message attached to it, i can not open it up. I can however open up pictures that are attached to email messages. i can forward the email message with the email attachment to another account or back to my original email address and access it through the web with no problems. so i am figuring it some thing within Outlook is causing this problem. There is no message in Outlook saying that it is blocked or stripped.
Any one have any clue as to what is happening here?
Thanks,