I can Save attachments, but cant open them in Outlook 2003

I receieve this message when trying to open attachments:
“this file may contain a virus that can be harmful to your computer. you must save this file to disk before it can be opended. it is important to be very certain that this file is safe before you open it”.
This messages appears no matter what file i try to open and I know there is no virus. I have tried editing the registry, but still get the same message.
When i save the file to a file I can then open it with no problem. I receieve so many attachments so its very annoying – I just want to open it from outlook!
Please, can anyone help?!