Visual Editor Not Working After 3.3 Upgrade

My visual editor tab is not working on two WP installations. I can see the Visual and HTML tabs but only the HTML tab / pane is active. I can’t switch to the Visual tab.

The first time I tried to edit a post the editor was on the Visual tab but the pane was blank except for some red underlines for misspelled words. I switched to the HTML tab to see what was happening and now I can’t get back to Visual tab.

I’ve deactivated all plugins and switched to the twentyeleven theme, with no plugins activated. No difference.

Not sure what else to do. Suggestions?