Blank email attachments

We have several site running Server 2003/exchange 2003 clients running Outlook 2003.
All sites are fine but one.
Forwarding several emails with attachments inside are being received blank.
Trolled through i dont know how many help topics sites now.
If we create a new user they are able to receive fine. Recreating the accounts is not an option due to the amount of applications and data they have set up.

Any thoughts.