Excel 2003

One of my staff attaches an Excel file ("Important Info") to an Outlook
email and sends it to a particular coworker. The coworker, upon opening, has
a file named "Copy Important Info."

This phenomenon occurs only between these 2 specific people and only in one
direction (person 1 to person 2). Is this an Excel problem or an Outlook
problem?

Any ideas?

TIA.