please tell us your exact steps that you've done to upgrade at what version of extensions you were using (before the upgrade).
Usually I would recommend to update extensions to a version that is supported by ePO 4.6.6 (didn't try 4.6.7) https://kc.mcafee.com/corporate/index?page=content&id=KB69814 BEFORE upgrading ePO.
e.g. if you were using HIPS 7.0 then you should update HIPS extension to 188.8.131.52.
(btw I think I would update clients too - in this case to 7.0 p9)
If thats the reason for your errors - I would recommend to roll back your epo to the old version (asuming you did a backup...) and try again.
The upgrade was a straightforward clisk setup.exe and perform an upgrade from the existing install.
I've checked the extensions and my products exceed the minimum versions except for VirusScan 8.7i which is a bit out, however I have no issues with that one.
HIPS wise, I'm using HIPS 8 Patch 2. I do have HIPS 7 extensions present from pre-HIPS upgrade but again both those and the HIPS 8 extensions are above the minimum recommended ones in the KB article you linked (thanks for that).