I had the same problem as everyone, and I tried deleting the the wp-admin and includes folders and uploading them again (as the upgrade guide says). That didn’t do it, so I deleted all the main wp files, modified and used the new wp-config file, and uploaded the 2.5.1 install main directory wp files. Basically, I did new install in a shortened form. I do hope the developers get this resolved, but thanks for the help.
