Thanks for the FYI. That will save me some head scratching next
time there is an update.

For now, my fix is to have executed Excel 11 on a command line
with the /regserver parm added. viz
"C:\Program Files\Microsoft Office\OFFICE11\EXCEL.EXE" /regserver

Dunno how it works, but now:
- Instantiating Excel returns 11
- I can still run 12 using Windows' Start menu
- Ditto 11

Only weak point - besides your observation - is that it doesn't
seem to work the other way. But instantiating 11 is all I need
for now, so I'm good to go..... as long as I remember to do it
again after the next update -)

Thanks again.

Per GS:
After serious thinking (PeteCresswell) wrote :
I need to test some stuff that is written for Excel 11, and
chokes on 12 (YIELD function).

I have both 11 and 12 installed on my developer box and, of
course, when the problem app instantiates "Excel.Application" it
winds up with 12 - even when CreateObject's argument is changed
to from "Excel.Application" to "Excel.Application.11"

BCO Office 12's security/copy protection scheme, it's a big deal
to get Office 12 installed on a PC in my environment or I'd just
uninstall 11, do my testing, and then re-install 12.

The Question: Is there a way to make 12 invisible to the system
so it acts as if 11 is the only version installed, do my testing,
and then revert to 11 and 12?

<FWIW
Unfortunately, v12 will be reinstantiated as the default version
whenever AutomaticUpdate installs updates. I hate when that happens!

What I do instead (on my dev box) is open whichever version I want to
use and open the project from within. I currently have versions 9
through 12 installed on this machine and I have no problem with
'default version' using Gord's suggestion via a '.bat' file. This is
very helpful for testing projects that use their own instance of Excel
via a VB6.EXE frontloader. What I found, though, is that v11 is the
only early version it (unreg/reg) seems to work with. IOW, with v12
installed I can't 'set' v9 or v10 to be the default when v11 is
installed. I'm sure it's doable but I don't care to spend the time to
figure out how since I can open any version from the Office Toolbar.
Also, you can run multiple versions simulataneously but you'll get the
warning about PERSONAL.xls being Read Only for each subsequent version
you open after the initial version.
--
PeteCresswell