ContentFilterVersion is a VALUE, not a Subkey. It is this value that SP2 is looking for.
It cost me quite a bit of time getting SP2 fixed, simply because Microsoft won't simply add the uninstaller to SP2, nor do they have it show up in add/remove programs globally (couldn't get it to show up in any Administrator account), nor do they have it available as a download to install so you can uninstall. Only to have someone point out the fact that this name is a VALUE and not a KEY.
Grrr!