"Your windows configuration cannot be upgraded"

Hi, When I try an in-place upgrade repair I get 'Upgrade disabled' - Your windows configuration cannot be updated'.

Details:

I've tried to do an in-place upgrade repair on my (99%+ working) Windows Home Premium SP2 + latest updates in the hope of fixing some minor problems, after extensive discussion with 3rd tier MS escalation support.

I've used a Vista SP2 DVD, dated 11-4-09 - which I think may not be an RTM version, as these folder dates are prior to SP2 RTM.

I also note from this forum (great guide) that all patches I have on my PC post SP2 need to be on the DVD.

I'm left wondering:
- how can I make sure I have a precisely matching current DVD and PC installation - or a DVD which is later than my PC installation.
- should I really have to uninstall all patches post SP2 to match an SP2 DVD?
- what precisely would give rise to "Your windows configuration cannot be upgraded" - I can't find this message on the internet.
- If the DVD is SP2 but a lower version number, would that fail to do an upgrade install?
- Is it possible to identify exactly what build number a Vista DVD is from the DVD alone?

Elsewhere (I think) I noted the requirement for at least 15Gb of free space.

Is there anywhere a clear user level spec of this process (by MS)?

Thanks!

My question has now become-

Which system folder path changes inhibit MS upgrade?

Ok, I've found a hint.. from an obscure MS document about upgrading from XP, not Vista, with exactly the same error message.

This message is generated if you have changed the path to a 'special' folder to another partition from C:\.

"This issue occurs because you put the "Documents and Settings" folder on a partition that differs from the system partition."

http://support.microsoft.com/kb/947240

Now, I have changed some, but not that.

So: which system folder path changes inhibit MS upgrade?
(there's nothing in my Setupact.log that tells me, alas. Hmm.)

The problems that you are having now and will have in the future is because of the upgrade. You are just hiding the old problems that will come back to haunt you. Make a clean install.
http://www.vistax64.com/tutorials/68767-clean-install-upgrade-vista.html?ltr=C

Almost all members would agree. Back up your stuff, bite the bullet and do a clean install. You will be amazed.

Mm, the problems are very minor.. like WEI doesn't (not uncommon- probably driver issues - 'New hardware detected') and a weird issue with a Firefox related registry string that gives me 8007002 when I'm routed to the old v6 MS update site by Vista Problem Reports and Solutions (which shouldn't be the case anyway- it's a hangover, I guess).

What I have come to suspect is that changing folder paths as supported by some tweak tools may preclude an upgrade.

For all normal purposes, Vista works. On that basis a clean install (very lengthy for me) is not needed or useful.

What worries me is the apparently flimsy nature of the 'in place upgrade repair' - it simply can't be relied on as in XP days. (oh, yeah, I do do disk images.....and routine registry backups...) and the apparent lack of specification. (Try finding much on 'Your configuration cannot be upgraded'!)