error 429: ActiveX component can't create object
 

I'm trying to automate an Excel program using vbScript. I'm running WIndows
XP Prof. (SP2), Office 2003(SP1), WindowsScript 5.6, and VB6.0(SP6). The Set
oPP statement below gives Error 429:
Dim oApp
Set oApp = CreateObject("Excel.Sheet")

If this were VB, I would add a reference to the Object Library to the
project. What should I do in vbScript?