After upgrading to WordPress 3.4, I could not edit pages or posts. The screen would be blank when attempting to edit.
I resolved this issue by reinstalling a bit differently. Rather than just overwrite the existing files with new uploads of wp-admin and wp-includes, I removed the old folders from the server first. I deleted wp-admin, wp-includes, and the other files necessary for installation (I did not delete wp-content or wp-config.php or .htacces).
Actually, some of those old folders wouldn't delete, so I ended up renaming them. For some reason they were giving permission denied errors when I tried uploading content. Not sure. No doubt this was the issue with the upgrade in the first place.
After removing/renaming the old folders, I uploaded new ones. Then went to wp-admin/upgrade.php and continued the upgrade. Worked fine after that. Pages and posts were no longer blank upon editing.