This happened to me also, to solve my problem I needed to go to TOOLS>CONFIGURATION select tab called >Interface & Features
Now scroll down and there is a tick box called Enable editor:
If that is selected as NO then this is your problem just need to tick the yes box hit save and your done.
That was my issue.
Cheers
Make sure that you uploaded the updated tinymce files. The updater only updates the plugin code in the database.
Re-uploaded everything, and did the install again. This time, selecting ’Upgrade’ and it worked ok this go.