I had issues with certain files not being found after my upgrade. I ended up deleting the installation and re-installing it. It worked fine until I re-copied over my modified "header-required.php" file that I had modified to call an additional script in the header section.

So if you have trouble with the upgrade, make sure you don't have any custom code in the /elements directory giving you problems. Try and rename those and see if you still have trouble. You might save yourself some grief.