Had a hard time nailing this down, but I *think* there is a bug in the way WP SEO adds its menu item in the toolbar.
WP Version: 3.4
WP SEO Version: 1.2.3
I did this: In IE7, visited pages on the front end while logged in, with multiple themes (including twentyeleven), and WP SEO installed. While viewing pages, and the "edit page" menu item and the "SEO" menu item are both active on the page, the toolbar stretches to two lines like this screenshot: http://cl.ly/0M1O2P0a0w2P2k2g4500
If I'm not on a page, and the "edit page" menu item isn't visible (archives, etc), the problem doesn't persist. http://cl.ly/1K3h0n1Q3i1j44303F3C
I do not get this error with WP SEO deactivated, or with other plugins that add a menu item.
Hope that helps,