I upgraded to 1.28.2 recently, but now I have found that my wiki will not display any page to visitors. It will just display a Permission Error instead.
The wiki can be found here: http://wiki.spheredev.org/Main_Page
It shows this error for all pages, including the login page. Luckily my session was somehow kept between upgrades, so I can confirm that all pages do display properly when I'm logged in.
Also: the previous version of the wiki ran on (really too many) extensions, but I tried configuring at least a few of the most important ones. Two enabled plugins are ConfirmAccount and ConfirmEdit, but I don't know if those are related at all.