Hi there,
I encountered the same issue, running WP locally with Multisite. I couldn’t find any solutions, but I did get to work when I left the plugins area and went back to the main dashboard. I got a pop-up warning about backing up my database, okayed that and then the upgrade worked. Hope this helps.
If that doesn’t work, go into phpAdmin and in the usermeta table, make sure wp_capabilities is a:1:{s:13:”administrator”;s:1:”1″;} and that wp_user_level is 10. Then try again.
