Thank you, & sorry to confuse. I am automating the installation of the
Hyperion program for a group of users and when they use Excel, they
need the Hyperion add-in to load. I have tried the various techniques
listed & seem to get limited success. The Hyperion program installs
fine, but this need to make the add-in work after the install runs is
kind of difficult to get automated post-install.

The weirdest way I've made it work is to creat 2 shortcuts, 1 to the
xll & 1 to the xla files & put them into the XLSTART fldr. I can
repackage the MSI to include those, but I would really like to be able
to do it in a cleaner, more viable manner. Possibly using the more
advanced functionality available in Excel. That is where I am needing
more help.

I'm not sure that what I did to load the add-in via the workbook open
code was the correct way to do it since it didn't work.
1. Right click on Excel icon top left corner, click View Code
2. In the middle box labled Book1 - This Workbook (Code), pasted the
following:

Dim oXL As Object, oAddin As Object
Set oXL = CreateObject("Excel.Application")
oXL.Workbooks.Add
Set oAddin = oXL.AddIns.Add("C:\HYPERION\essbase\bin\essexcln.x ll",
True)
Set oAddin = oXL.AddIns.Add("C:\HYPERION\essbase\bin\essxleqd.x la",
True)
oAddin.Installed = True
oXL.Quit
Set oXL = Nothing

3. When I exit it wants to save the changes to Book1, but I'm not sure
how/why/where to save this so that it runs everytime Excel is opened,
so I tried saving it in the XLSTART fldr (I also want to make sure it's
loaded for all the spreadsheets in the workbook)

4. Reopening Excel after that didn't result in the Add-in being
loaded.

5. I also tried the same thing using this:
Private Sub Workbook_Open()
AddIns("C:\HYPERION\essbase\bin\essexcln.xll").Ins talled = True
AddIns("C:\HYPERION\essbase\bin\essxleqd.xla").Ins talled = True
End Sub

6. Saved it into XLSTART & on the relaunch of Excel, there's a MS VB
Run-time error '9': Subscript out of range, the debugger shows a
failure on the 2nd line. The AddIn isn't loaded.

at this point i'm stuck.