Mac computers having issues opening attachment from outlook 2010 but not on outlook 2003, need help.

I'ved send email to multiple clients with attachment(mostly JPEG) using outlook 2010, the clients that are using MAC computers can see the attachment as attached but when clicked it gives a "file empty error", This only happens on Mac computers, but when we try sending the same email attachments from outlook 2003 there is no issue.  Is there like a new security feature on outlook 2010 that I can turn off to fix this situation.  This is obviously not a Mac computer issue as they can open the same file attachment from an older version of outlook.  Thanks in advance.