Actually I had some similar problems with the upgrade to a previuos revolution release:
-I migrated my website to a new server, everything was working fine.
-After sometimes, I had to upgrade MODx and I found some problems with the process (if I remember correctly a blank screen during the process).
- I checked and changed the folders permission: the setup-upgrade process worked fine, but as soon as I logged into the manager I found out some blank screen again...Not everything, but some section of the manager.
- so I changed some other folder permission, I don’t remember exactly which folder caused the problem (may be controllers, or connectors, but really I don’t remember).
Anyway after setting some folders to the most un-secure 777 I solved the problem...
After that my system administrator "cleaned" folder permissions setting ownership and writing permission correctly, at least I hope so