This is similiar to a problem I am having. Windows 2003 Server is far more
strict when it comes to what users/identities can run which applications.
The only thing I've come across is references to the DCOM Config of the
Microsoft Excel Application.

Here's what I did:

On the Windows 2003 server, start Component Services from the Administrative
Tools. Open the Component Services tree, open the Computers tree, and open
the My Computer tree.

You should see one or more of COM+ Applications, DCOM Config, Distributed
Transation Coordinator and Running Processes, and maybe others.

Open the DCOM Config tree. Scroll down to Microsoft Excel Application,
right-click it and select Properties. Click on the Security tab, and in the
first frame (Launch Permissions), click the Customize radio button and then
click on the Edit... button.

In the Launch Permission dialog, click Add... and add the NETWORK SERVICE
account. Click OK, close all the dialogs and reboot the server just to make
sure the changes take.

Try your app again.

Hope this helps.

Regards...Andrew