Ever since the 3.5 upgrade, I can't select all plugins or themes in the WordPress updates are or select all plugins in the Plugins area.
I have tried disabling all plugins to make sure there wasn't a conflict. Problem remains.
I disabled all Chrome extensions - problem remains.
I changed to 2011 Theme, problems remains.
I reset my plugins - problem remains.
(Note: Doing this causes you to lose the "recently active" from your plugins menu so you will need to remember which ones you had active. What a pain!)
I have NOT tried re-uploading all the files because as another poster said, that seems like a big pain. The only solution I've seen is offered in this thread: http://wordpress.org/support/topic/35-select-all-doesnt-work-in-update-plugins-area?replies=3
But there has to be a better solution that having to reupload all of the wp-config files with that line of code in it.