Lotus/ ACT Contacts/Exchange

I have a user here who is having trouble sending someone attachments.
Our company is using Exchange with outlook 2000. The person that he is trying to email is using Notes. My user is using ACT Contact manager, and everytime he sends a contact of his an attachment, the attachment gets completly decoded. No matter what kind of an attachment it is it doesn’t get transfered right. It turns into a dat file, and is all wierd looking. This only happens when he sends to people using lotus notes. I have sent attachments to the same people from the same exchange server, and they work fine. Any suggestions?

Thanks!