I was having EXACTLY the same errors as this guy—basically, none of the javascript elements in Wordpress were working, ex. Check All Checkboxes, multi-file uploader, text in the post editor was "invisible," etc.
How I fixed it:
- Delete all the files & folders in your "wp-includes" folder.
- Re-upload all the files & folders in the "wp-includes" folder.
- If any of the files failed to transfer, put them back in the transfer queue and send them again.
SUCCESS!