[eluser]TheFuzzy0ne[/eluser]
How have you done the upgrade? Did you completely remove the old files from the system directory, or did you just copy over the existing ones?
My suggestion would be to totally delete the system files first, and then try to install. If the problem still persists, it's most likely something to do with one of your configuration files, in which case, as painful as it may seem, I'd recommend you compare your current configuration files to the new ones, and see look for anything that might be out of place.
Obviously, it goes without saying that backups need to be made first.
If you follow the steps above, it will rule out any anomalies with the core files, and anything to do with your configuration.
If the problem still persists, then it may be time to check out any classes you may have extended (although it's unlikely there should be any problems there).
It might also be wise to create a test controller and a few very simple test views, that will mimic your current set up on a more basic scale. If the problem still persists, share it with us, and we will see if we can confirm any issues.
I'm willing to bet that your problem will most likely have something to do with incompatible configuration files of some kind.
Best of luck!
