Cant open excel attachment Outlook 2003

I am currently running windows 2000 pro with office 2003 basic. When reading email using outlook 2003 with an excel attachement I am unable to open the exel file. When you dbl click on the attachement excel tries to reinstall. All other attachments work fine. You can save the exel file to disk and open it. How can I resolve this? Any help would be appreciated.