Hello Gerard,
Do you run WGsetup.exe on all machines? It creates the
file association for the *.mtm format.
From MS Project 2002 Help:
Set up an e-mail system for team collaboration
To use an e-mail system to send and receive team
collaboration messages, you and your team members need to
run WGsetup.exe.
1 Copy the entire WGsetup folder, found on the Microsoft
Project CD-ROM, to a network drive that can be accessed
by everyone with a MAPI-compliant, 32-bit e-mail system.
2 If necessary, you or the team members can connect to
the network drive that contains the WGsetup folder by
using Microsoft Windows Explorer.
3 In the WGsetup folder, double-click WGsetup.exe, and
then follow the instructions when prompted.
Hope this helps.
Julie