Outlook cannot open Excel XP attachment

Key points:

1. Senders have Office XP.
2. Recepient has Office XP.
3. This problem only happens with Excel and only to one particular user.
4. This has happened to the same user on two different PCs with fresh installs on each.

The user will receive an e-mail with an Excel attachment but when she double clicks to open it, Excel opens up but there is no file open, just a blank screen.

If she saves the attachment to the hard drive then she can open it just fine. It only fails to opendirectly from Outlook.

She is running Windows 2000 SP3 with all the latest updates from MS, Office XP SP2 and the latest BIOS updates. Same results on 2 different PCs (see above).