Installed the upgrade version 3.9 and I've had nothing but PROBLEMS. Deleted it and all files, 3 times now, reinstalled and still having the same issues. On any browser, the media button, screen options button, editing do not work. I have all functions UNTIL I update the page or post and then 'pouf' it's all gone, no editing options and the buttons do not work. I've disabled ALL plugins, still same issue. Spent hours on the phone with my hosting company, BlueHost. My site has been down now for a week. I also have 4 other sites that run WP and were upgraded to 3.9 and are doing fine. But my fresh install of 3.9 does not work. HELP. With all the installation problems with this version it seems that there should be a fix by WordPress available. Again, another fresh install and in uploading a new theme I receive this error: An unexpected error occurred. Something may be wrong with WordPress.org or this server’s configuration. If you continue to have problems, please try the support forums.
Needless, to say I am more than frustrated. The other sites I have are working fine with the same exact theme and plugins. My plugins are all deactivated and a fresh install of 3.9 and again.... problems.
I found this answer on another post:
Try re-uploading all files & folders - except the root wp-config.php & .htaccess files - from a fresh download of WordPress. Make sure that you delete the old copies of files & folder before uploading the new ones.
But I do not know how to accomplish a re-upload without including the files mentioned.
I also found this solution:
Looks like I've just sorted it. I followed the instructions in step 2 on the page below and it looks much much better. Just had to enable script de-bug in the wp-config.php
I completed it and I'm still having the same error in even trying to upload a theme:
An unexpected error occurred. Something may be wrong with WordPress.org or this server’s configuration. If you continue to have problems, please try the support forums.